Beginner DAC/AMP recommendation for HD 600 Sennheiser's

[AnalogSteph]

Will this C200 dac/amp drive BD DT880 250 Ohm?

These are in the same ballpark as HD600s, a bit less sensitive but less impedance-critical as well. Can be driven by most anything with half-decent output voltage. So no worries.

Oh, I missed this post:

I enabled it this morning and hooked up the HD 600's direct to my PC as opposed to the SMSL C200 and holy hell the onboard audio drives the 600's INSANELY loud. The motherboard specs are as follows:

Mobo: ASUS z370-F
DAC: ROG SupremeFX 8-Channel High Definition Audio S1220A
AMP: Texas Instruments RC4580 and OPA1688 OP1688 op-amps which can drive up to 600ohm
RMAA Performance of 113db

Congratulations, you've got some Fancy Onboard Audio™. (I would assume that the OPA1688 is only for the front panel output but check the manual if in doubt.) Presumably you'll get something like 2 Vrms out of that, which as you noticed is plenty loud with these cans. The chip also has a native output capable of 2 Vrms, probably that's routed to the back panel.

Edit: On further listening there does seem to be a difference on the standalone amp compared to the motherboard, seems there may be a lot more to it than just volume. That or I need to check in to a mental asylum.

You may have to turn off some custom driver-side audio misimprovements that may have been enabled automatically for headphone use (BTDT). Also, output impedance does remain as a variable, 75 ohms should make the low end slightly fuller. I don't think shared ground resistance on the front panel cable would be high enough to pose any kind of issues with 300 ohm cans.