I've been through several sound cards, trying to achieve the best recordings. (buying/selling, etc)
The 2 main criteria which seem to affect D.I. recording quality are preamp sound quality, & audio latency when record monitoring using ampsims/cabs. If you can't record & have it playback TIGHT, it's never going to sound pro. The lower the glitchfree latency, the more accurate you can play in time, & the more likely the DAW will play it back in time. One problem is the driver settings for different units often use different terms for their settings, some are samples, some are milliseconds, so how do you compare? Wish I had tested all the units I've owned, but just found this free latency tester utility:
http://centrance.com/downloads/ltu/
The method to test is to run a patch cable from the interfaces output to the input, the utility plays a short signal, and measures the roundtrip audio latency delay.
Test results using the CEntrance Latency tester:
I Set the soundcards drivers to the lowest glitch free record monitoring settings. Example- a Reaper session running 2 basic guitar tracks w/fx (one set for record monitoring), EZ drummer, & no other fx in the session anywhere to slow it down. Guitar tracks were noise gate/loner or legion/boogex, no other fx on. Then ran the latency tester, using that same buffer size/latency setting.
Presonus Firestudio Mobile, '128 samples buffer size':
32000 hz sample rate = 431 samples/13.47 ms
44100= 455/10.32 ms
48000= 463/9.65 ms
96000= 590/6.15 ms
Creative Sound Blaster X-Fi pci-e card, '5 ms ASIO Buffer Latency':
32000= N/A
44100= 899/20.39 ms
48000= 923/19.23 ms
96000= 1863/19.41 ms
Line 6 GX, 'extra small/128 Samples buffer':
32000= N/A
44100= 852/19.32 ms
48000= 869/18.10 ms
96000= N/A
At least on my system, the Firewire device outperforms PCI-e & USB. In case you want to compare computer specs:
W7 64 bit PC, AMD 2.9 ghz, 6 gb ram
Hope this info helps someone.
Anyone care to test their cards?

