"If neither approach seems to work well,is there another way?"
Yes, use both approaches.
I use the quick A/B comparison to spot any immediate weaknesses that would annoy me long term. ;-) Really. If one DAC stands out as lacking something I desire, the quick A/B comparison quickly reveals it especially if the two DACs sound noticeably different, and some do.
Beyond that, if I find both DACs to sound outstanding by my initial standards, I'll listen long term to determine the 'winner'. In some cases it's a toss up and I'll keep the less expensive DAC.
Many good DACs will not exhibit significant weaknesses but may be 'voiced' slightly different by their respective designer. IMHO many buyers place too much emphasis on which latest DAC chip of the month is listed on the manufacturer's marketing slick. There have been many excellent DAC chips available in recent years and it's up to the designer to get the most out of it including the very important analog output stage of the finished product.
A couple A/B losers that I threw out in short order:
- Luxman DA-06 DAC
- Wavelength Brick USB DAC v3
Both of these were very 'smooth' but noticeably rolled-off at the frequency extremes. A case significant weaknesses immediately revealed in a quick A/B test against a couple other DACs I had.
