Smith-Morra

The line must be Dubious. Analyze with Stockfish at least Depth 30.

6 ...a6 is very interesting, but the most reliable way for Black to equalize (at least) is the rarely seen 6...Bb4!

Black is threatening to take on c3 at the correct time and then play ...d5 and equalize (not immediately however), depending on how White replies. But this sets a trap that can bait a VERY poor move that will get you some free rating points : White chasing the bishop pair with 7 a3? (a blunder). Then 7...Bxc3+ 8 bxc3 Nf6! creates a double attack threat of both ...Nxe4 and ...Qa5, so 9 Qe2 (Qd3) does not solve White's problems, to 9...Nxe4! 10 Qxe4 d5 with advantage to Black, and 9 e5?! is even worse after 9...Qa5 with another double attack. (10 exf6? Qxc3+, and 10 0-0 Nxe5, and White is not happy.)

After 7 0-0 Nge7 8 Qe2 0-0, or 7 Qe2 Ng7 8 0-0 0-0, White has to make some decisions on how to proceed. 9 a3?! (again) Bxc3 10 bxc3 Qc7 11 Rd1 d5 is not what White wanted, 10 Bf4?! Ng6 11 Bg3(?!) (11 Bg5? Nd4!) Bxc3! 12 bxc3 e5! with the famous "locked out" bishop on g3 simply leaves Black up a pawn, and 10 Bg5 h6! 11 Bh4(?!) Qa5! with the idea of 12...Bxc3 followed by ...d5 cannot be stopped, so better is 11 Bf4 a6 followed by ...12...b5 if allowed, and Black is happy.

Maybe 9 Rd1 is best, but after 9...Ng6 10 Bg5 (otherwise Black plays ....a6) Be7, White has nothing.

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About your ...a6 line, this can lead to setups like ....Qc7 and ...Bd6 followed by ...Nge7. This is about equal in overall evaluation as the ....Bb4 line I mentioned, but ...b5 is a lot more committal so it's a matter of style and preparation.

This line is not dubious. I've analyzed this with Stockfish with a core i9 14900k (32 threads). Of course with best play, every single line less than +1.00/-1.00 always ends up leading into a draw of some sort (including pawn down rook endgames), but 8 Bb3?! is not the correct move, because of 8...Na5. 8 Bd3 Bb7 9 Bf4 is stronger. Keep in mind the smith morra is not a fully sound pawn sacrifice--White is struggling just to equalize fully.

Bd5 is a bait that doesn't threaten anything. Black can simply ignore the bishop and play ...Bb7 followed by ...Ng8-e7, then White has to start thinking very carefully about that bishop on d5.

8 Bd5 Bb7 9 Qe2 (what else?) Nge7 (...Nf6, ...Rc8, ...Be7 and ...Bd6 are all interesting possibilities) 10 h4 h5 11 Rd1 Ng6, and what does White have? He still isn't even fully equal.

9...Bd6 is quite nice too. 10 e5 Bc7 11 Bg5 Qb8, and now white MUST move the bishop on d5. 12 Be4 Nge7 13 Bxe7 and either ...Nxe7 or ...Kxe7(!) (13...Kxe7 14 Rad1 h6 (guarding g5) 15 Rfe1 Rd8 still leave White fighting for *equality*.

It's Black who should be fighting for equality, not White.

It's hard to find a good path forward because White is not even fully equal! One of the qualities of having a slightly worse position is the inability to find anything but an equalizing plan, by making common sense or tactical moves that put pressure on the opponent, or to otherwise sit back and wait for your opponent to blunder while not making your position worse. You're trying to "make progress" in a position where you do not have full compensation for the pawn. Making progress, as you are thinking of it, requires you to have the initiative, which you do not have. You just have more space and some open lines, but no clear targets (e.g. something on the dark squares which can transition to the light squares) without forcing undesirable exchanges. The reason for that is because Black's pieces are also well placed to deal with any aggression. With absolute best play, White can usually force Black to return the pawn, and then try to get an endgame that ends up fully equal, but you're not getting any more than this.

The above line was supposed to be the crushing line which completely destroyed the Smith-Morra.

The Smith-Morra was considered unsound due to the above line which is very engine like, but very effective.
In Fact, The leading expert to my knowledge was a man named Esserman ( Who was a National Master at the time). The last time I remember talking to him about the line was on the Chess Forums many years ago and he got the norm’s to gain IM Title. He showed the calculations on how White could hold the draw if I am not mistaken. If you like Smith-Morra, you should Buy his books. He has the in depth Information you need to play the Smith-Morra better. I didn’t buy the books because I have no interest in helping white play better. I’m not Smith-Morra fan boy.
My goal was to gather intel on my rival opponents who are foolish enough to play this line. It is very important to know what your enemy is doing so you can more efficiently destroy them.

So you say you are struggling against this simple Sicilian Kan line? Maybe, I should investigate this as another option to crush white. My first impression is not good. It looks like Black is going to get mated here. The line looks to easy for white.

Look at the whole board

White is castles with 3 pieces out.

Black has 1 Knight + will take like 3 moves to castle.

Is Black just getting checkmated here? It’s actually a valid question. Can white literally sac everything and win with the lead in development they have?

Did I recommend this line? No. It's dynamically equal but Black is NOT getting "checkmated." Eval is 0.08, which is good enough to be called "unclear."

The strongest line for Black to get a comfortable game is not ...d6 but ...e6. this leads to a structure similar to what GM Polgar used to play (with ...Nge7-g6), usually starting with 4...e6 and 5...Nc6, which is directed against the 6 Bc4 variations (which are almost played automatically), 6 Bc4 Bb4(!).

Of course there are alternatives like systems with ...a6.

I consider an opening "unsound" if it's White, who has the first move, who is trying to get equality, rather than Black.

My comment wasn’t directed to you.

I was commenting towards the OP.

I know you showed a different line.

The line the OP is showing is interesting.

It looks very risky and sharp.

It looks like Black will have to play a string of precise moves to not get checkmated. 
The engine says position is fine for Black because it probably knows the string of moves Black needs to play to survive the position.

Black has few pawns developed with 1 Knight out and no hopes of castling in near future.

White is fully mobilized ready to attack.

1 Slip up or 1 Forgotten move by Black is all White needs to deliver the checkmate.
It is interesting to talk about though.

It also seems like you are recommending a different way to play for Black involving Bb4 move.

@1

Here is a top correspondence game from 2013. White can hold the draw.

Esserman has 102 games from this exact position on Lichess.

Search in explorer by player. His username there is MassterofMayhem.

If the OP plays a better opening, he wouldn't have the problem he's having. The Smith-Moron Gambit is trash!