for that opening, see scotch gambit
2 knights defense - d4 viable?
that move order is not the max lange. the max lange arises after 1. e4 e5 2.Nf3 Nc6 3. d4 exd4 4. Bc4 Bc5 5. o-o Nf6 or transpositions. other moves are not a max lange. since white played 5Nxd4 the position is just a bad two knights.
there is no such thing as the max lange attack declined: it either is a max lange or it isn't. The move you give for the Max Lange declined, is called the Morphy attack.
The OP seems to haved asked about 5. Nxd4 which doesn't seem as good as the more common moves.
Better tries might be 5. o-o (at which point you're in serious danger of people arging whether or not you've entered the Max Lange Attack.)
or 5. e5 which I think is the main move.
Also stuff like 5. Ng5, 5. c3 are lines but probably not such good ones?

there is no such thing as the max lange attack declined: it either is a max lange or it isn't. The move you give for the Max Lange declined, is called the Morphy attack.
There is an Anti Max Lange. You could consider it the Max Lange declined if you were so inclined.
The reason why I don't think 5. o-o is as good as 5. e5 is because of this line which does avoid the Max Lange where or not you want to call it a variaition of the Max Lange.

"Strong players have told me Qh5 is a drawing variation and Qa5 is more ambitious."
Interesting since I was looking at both options this weekend and trying to decide which one I thought was more playing for a win. Qh5 seemed to be my preference. Looking at the CT database, Black has the same win %, but the draw rate is increased. So it seems like Black has the same chances but White has less against Qh5.

Black has a big problem after 5.0-0: Which move should he pick after 5...Nxe4 6.Re1 d5 7.Bxd5 Qxd5 8.Nc3 to retain winning chances? The choice between 8...Qh5 and 8...Qa5 isn't easy- both seem to lead to objective equality.
Maybe it's time to switch to something odd, like 8...Qd8, or the strange 8...Qd7 which so far is quite succesful in correspondence chess.
But honestly, white cannot even dream about the slightest of advantages in that line: he definitely plays to make a draw, and he usually succeeds.
I like Qh5 and play it myself but my games are full of mistakes. There's a website with good free coverage on those lines... let me see if I can find it. http://tws27.weebly.com/scotch-gambit-4nf6-50-0.html
(edit: posted before I saw Pfren's post)

I like Qh5 and play it myself but my games are full of mistakes. There's a website with good free coverage on those lines... let me see if I can find it. http://tws27.weebly.com/scotch-gambit-4nf6-50-0.html
(edit: posted before I saw Pfren's post)
I also played 8...Qh5 the last time I had the choice (a few months ago) and won easily, but the opponent went wrong immediately with 9.Neg5?! (the right move is certainly 9.Bg5 with eventual equality- a few analysts tried to prove an advantage for Black, but IMO they weren't succesful).
The site you mentioned fails to notice 8...Qd7. It's the move advocated by Ntirlis in his recent QC repertoire book, as well as in a chess.com Dzindzi video:
https://www.chess.com/video/player/giuoco-piano---part-1-two-knights-defense
Hi guys!
All through high school, I played the opening:
1. e4 e5
2. Nf3 Nc6
3. Bc4 Nf6
4. d4
Now that I play it now adays, I always get my e4 pawn killed by the knight and I am at a disadvantage after:
4. ... exd4
5. Nd4 Ne4
Now, that Ne4 move makes me down a pawn. I don't want to admit that the d4 move for white is bad because I've played it forever. Is it time to give up this move, or is there something I don't see as white that gives equalization after a few moves?
Also, does anyone know if the 4. d4 move has a named opening?
Thanks for the help!