Probably the most difficult of my crosswords so far...

Answers so far:

Across: 1.Miles, 3.Barleycorn, 5.Bird, 7.Regence, 10.Taimanov, 11.Sliwa

Down: 1.Mecking, 2.Bogart, 4.Lilienthal, 6.FEN, 8.Sicilian, 9.Norms

1 A Mles

4 A Bird

7 A Regence

8 D Sicilian

9 D Norms

 Wow, I'm impressed! Miles is just a fingerslip I gather...

Yeah, Miles : )

Immortal losing game winner?  That's a little cryptic, lol

6 down is fen?

 Yes!

1 down is Mecking.

Correct!

 11 is Sliwa, 4 is not Korchnoi.

4 down is Lilienthal.

Lilienthal is correct.

3a barleycorn

10 across is Taimanov.

 Yes!

 Correct!

2d bogart

gah another one?! lol.

 Correct!

Thanks to everyone who helped solve!