What DAC were you looking at?
Personally, I find the appeal of the 2170 to be its transport-ability. As such, I'd think a portable DAC or DAP would be a suitable travelling source solution. I use the FiiO X5 -> SRM-252s like this on occasion. I'd like to see someone try packing a 009 with a BHSE, or any of the bigger STAX energizers, on an airline carry-on.
That being said, I currently have a desktop TEAC UD-H01 USB DAC feeding the SRM-252S. I'm satisfied with this combination. I'm inclined to think it can already render most, if not all the detail present in the source material (based on my familiarity with the tracks being listened to). Would be interested to A/B other DACs at some point, just to see.