Craig, Mike brought up a good point.
To effectively play/monitor in realtime thru software based processing/EFX, round-trip latency needs to be sub 6ms.
Upward of 10ms feels like playing thru molasses... (or a masochistic 100% wet delay line that can't be bypassed)
The little RME Babyface yields sub 5ms total round-trip latency at a 48-sample ASIO buffer size 44.1k.
That's dangerously close to the best PCIe units.
RME are the (low-latency) benchmark by which all other USB audio interfaces are judged.
RME has earned that "benchmark" status.
With a well-configured current generation machine, you can run substantial loads (glitch-free) at that 48-sample ASIO buffer size.
IMO, Tascam needs to achieve this level of performance to attract the masses (if you can call our niche massive).
Great fidelity with rock-solid low round-trip latency... paired with great support and easy install will result in sales.
I wish you all the absolute best... just kicking my $0.02 into the discussion.