Interconnect or USB cable

great point audphile1, thanks. here's my system:

Primare i30 integrated amp, Ascend Acoustics Sierra 2EX speakers, Rythmik L12 subwoofer, Triode Labs American speaker cables, Audio Envy Studio Prestige Interconnects and Power cords, Acoustic BBQ Full Rack USB cable, Schiit Bifrost 2 DAC

Depending on how much you were planning to spend….

The best USB cable I have tried is the Audience AU24SE+. 
What to upgrade first? Tough to say…if you get better ICs you can only realize as much as your DAC and USB cable can dish out, and other way around if you upgrade USB your ICs may become a bottleneck. 
 

In my opinion, best way to approach it at this point in your system is to upgrade the DAC. Forget cables for now. But again, just my opinion. 

Me’all?  Neither. I’d get another sub first. I think that will give you the most significant improvement.

 the sub matches with the speakers and is very good in my room so thats not leaving but thanks for your idea.