Good thread and good points given!
As to anyone considering getting a USB-connected DAC\AMP (the majority on the market....a few are still available in Firewire) I would add these pointers...…………..
If getting a USB DAC\AMP that is bus-powered (the focus is on the DAC\AMP section of external audio interface being powered thru the USB port), make sure that the MB USB port that you're plugging it into can supply ample power to sufficiently drive the AMP along w\ the DAC so that the interface will work properly. The best remedy for this is to
use a MB that is equipped w\ USB ports that are dedicated to be used w\ audio output (DAC\AMP's) as these have the necessary extra power supplied to them (some MB's....such as Gigabyte MB's.....have these dedicated USB DAC\AMP ports in which the power output levels can be adjusted thru the UEFI to accommodate the power requirements of various USB-powered DAC\AMP's) along w\ well built circuitry to maintain stable power delivery across the USB cable to the DAC\AMP. If these type DAC\AMP's are underpowered and\or the power delivery to the DAC\AMP is not stable the sound output will not be good and will suffer all kinds of distortions. USB-to-PCI-E adapter cards won't cut it as well due to lack of adequate, stable power delivery for good sound output (been here, done this) so I don't recommend them for sound. If you don't have a MB w\ dedicated audio USB ports and you still want to use a USB-powered DAC\AMP, then the choice of headphones w\ separate mic or headset's impedance level (where the DAC\AMP's power output will come into play)will become more crucial to good sound output......rule of thumb is to not use more headset\headphone w\ mic than the DAC\AMP can adequately drive w\o distortion. The higher the impedance level of said headset\headphone, the more power is needed to drive the speakers properly to reproduce a good clean sound wave.
Of course, this last statement is SOP regarding good sound output as any sound processing should be looked at as a system and all components should be properly matched up for the best processing output w\ the weakest point always being the sound processing source (where the sound is initially created and\or processed). In this regard the system sound source is AHIII's FMOD and no other part of the sound system...if properly set up...should diminish what is coming from the game's sound processing software, only should enhance it if needed.
The best option w\ USB DAC\AMP's is to get 1 that is self-powered (DAC\AMP has it's own dedicated external power supply) so that the DAC\AMP will not be underpowered and will always have stable power circuitry so that the DAC\AMP will perform to it's best. This will also open up the impedance range so that you can properly drive equipment w\ impedance levels up to 600 ohms w\o fuss or distortion (here is where most discrete PCI-E sound card AMP's will fall short due to power limitations of the PCI-E slot..300 ohms is the usable limit from my experience though most advertise 600 ohms range....been here, done that as well...). Then the only item you'll need to watch out for is which type USB port you plug the DAC\AMP-to-PC interface cable into....again this is due to power stability. Most USB DAC\AMP's currently out were designed\built to a USB 2.0 port's power standards to carry the digital sound processing signals from the PC to the external DAC\AMP and will work well. If this cable is plugged into a std USB 3.0\3.1 port, the DAC\AMP may run into issues w\ power instability across the interface cable due to the USB 3.0\3.1 port trying to set\retain the backward power output capability to USB 2.0 stds that the DAC\AMP was designed for causing the hissing, popping and crackling noises thru the speakers (been there, done that). Again, the best option is to
use a MB that is equipped w\ dedicated USB ports designed for audio output as it doesn't matter whether these ports conform to USB 2.0, 3.0 or 3.1 power stds....the power output delivery is STABLE and CONSISTENT thus none of these issues occur. The next best option is to use a std USB 2.0 port off your MB (if your MB still has them) to attach the USB DAC\AMP interface cable to your PC to stop this from happening. Again, a USB-to-PCI-E adapter card ain't gonna cut it.
Just putting this out here to give some help to anyone who may be considering to go the external USB audio DAC\AMP route to avoid these simple issues as IMHO, if you want the best sound experience from AHIII's FMOD system, you need to upgrade to an external DAC\AMP (at least a discrete PCI-E sound card) that has an onboard DSP that can provide or enhance good 3D sound positioning along w\ a good set of headphones, headset or speaker system for the DAC\AMP to be able to cleanly drive the analog sound output to for playback.
I can guarantee you, if you ever experience this 1 time w\ a good external DAC\AMP w\ onboard DSP setup you will never want to go back to anything less.