max4298I think you're expecting too much from 3-inch drivers. Of course you'll get a fuller sound out of, for example, the JBL 305 monitors at $300. But it's also more difficult to fit JBL 305s on a desk with a PC tower, monitor(s), keyboard and mouse. Sometimes reduced size is a benefit, as long as you don't expect profound bass or high output. And not many computer speakers offer a non-proprietary, line-level summed mono RCA output allowing you to add any subwoofer you choose. PSB has acknowledged the biggest shortcoming of mini monitors and provided a subwoofer output to address it. If you aren't using a subwoofer, you aren't doing it right.
If you're struggling to find the sweet spot, try positioning the speakers farther apart. I've got them about 45° with a toe in directly toward my ears. I have freedom to move back and forth and side to side without profoundly disrupting the sound stage. Also, make sure the speakers have room behind to breathe. They need to sit at least 6 inches from the wall I think.
The USB port is intended for an external Bluetooth receiver. It cannot be used as a DAC or for power, I don't think.