bit-perfect 24bit SPDIF or optical?
Sorry for nit-picking but there's some terminology confusion here. S/PDIF is the signal format, optical (or coax BTW) are interfaces/modes to transfer that signal.
http://en.wikipedia.org/wiki/S/PDIFI know you mentioned MTII, but MTI (aka MT 24/96) could also be mentioned as a separate entry, right. Although it's marred with issues.
So the updated list goes (ascending street price)...
24bit:
MT2496 ( very unreliable)
MTII (unrealible)
generic laptop + VXpocket or EMU 1616
Macbook or Powerbook G4 Alu
D50 (although incompatible with older gear because of flag issue)
PDAudio CF card + assorted PDAs
671
661
DR-680 (flag issues too, AFAIK)
Other pricy/bulky recorders like R-44, HD-P2, SD 7xx series...
16bit:
JB3
H1x0
670