Hey Fred,
The goal is to have 2 in, 2 out, MIDI, and maybe digital coax plugs.
Full duplex, integrated DSP, ASIO2, latency "zero", 24bits/96kHz ability
have to be there.
Although you covered allmost all the details there's one or two more important factors:
-FireWire or USB?
-Internal or External ok too...?
If FireWire and External are ok, an AudioFire 2 from Echo is exactly what you describe above:
2 in, 2 out, MIDI, S/PDIF.
It doesnt have onboard DSP... but I dont know if you really mean an onboard DSP chip with that..?
It is "full duplex", but expect that from any soundcard these days, and it does 24bits@96kHz, 2ms
on an RT kernel recording on a modest laptop.
Due to it using FireWire, you need the FFADO backend for JACK. Check ffado.org for details & support levels.
(The Echo is fully supported.)
Its worth checking out I think, Hope to have helped, -Harry