I'd highly consider something like the RME ADI-2 DAC.... its USB is outstanding and the sound is WAY better with Blu-ray pure audio discs than my Oppo BDP93, even though the ADI-2 can only play it @ 16bit/44.1kHz versus the 24bit/96k it should be (using digital coax because no HDMI input available)... much fuller/richer, and clean, with BLACK background...the OPPO really sounds BAD compared to it. DVD-A media plays at 24bit/96kHz through it from the Oppo though, so I also assume it will at the max 24bit/192kHz as well. RME ADI-2 DAC will do up to 32bit/768kHz / DSD256 over USB...
Plus the built in 5 band PEQ, crossfeed, tone control knobs, balance adjustment, and fully adjustable/customizeable feature set makes it completely outstanding DAC...and add to that the amp section which is great as well and you have an increfible DAC/amp with unheard of features and custimization for $1k...All in one rig DAC solution that can cover non-Electrostats as well with the headphone and separate dedicated IEM jack...
I just downloaded the Boston 'Third Stage' album from HDtracks in 24bit/96kHz FLAC late last night, but didn't listen to it on my STAX rig, was on my bedroom TH-X00PH centered rig. Very nice sounding, but don't have CD album to compare it with to see what difference there is. Want to listen to it tonight on my STAX rig.