i own both an ewx 24/96 and an ews64 xl, because of the isa slot problem. because ewx and 6fire have the same drivers (it's all based on ews88 technology) i think you will have as few problems as i have. the input noise ratio (measured with cool edit pro) is about -85dB at 44.1kHz, a value i never reached with the ews.. but midiman cards seem to be even superior (better than 400?+ cards with external ad/da boxes), i read it in a comparison between hoontech dsp24 value and delta audiophile, unfortunately i don't have the url anymore.
my only reason for my ews64-in-a-p150-desktop is its stability. unfortunately the ewx24/96 lives inside a athlon xp on via kt266 chipset, which has lead to some unreproducable crashs, even with newest via drivers and latency patch installed. i would never take this one to a gig as the only sampler =).

greetings, Matthias