probably the same (or similiar) Converters as in a Pulsar One ...
the weak point is usually (as gary mentioned) the micpre part of the channel
with a good pre in front of it and solid line level it's a cool box.
as my A16 gets a bit noisy from time to time (intermediate spikes) I recently replaced it by a Korg Soundlink AD/DA 880 couple
(which happens to be the exact same chips, but it's circuit diagram is available online)
all this 24bit (input) talk is pretty pointless imho
to take advantage of at least 20 bits you'd need a four-figure preamp under all circumstances
(or show me the one with an effective noisefloor lower than -100 dB)
I don't believe in the headroom talk at all, as conerters are linear devices adjusted to a voltage range
(which is linearily divided in bits per voltage - it can never exceed this range and won't ever clip 'digitally')
worst case would be analog distortion
for me there's no problem to have an 18bit converter that delivers a perfect 16-bit signal (valid to the last bit)
(the Fostex has 20bit Converters on the input side iirc)
I don't have any gear with less than 90 dB noisefloor anyway

so I take advantage of modern marketing blurb and buy the cool old stuff...
cheers, Tom