I have owned a Theta Miles (balanced version-twice as many DAC chips as RCA only version) and the Cary Audio CD-308. I ran both directly into a plethora of amplifiers. Both worked great.
Currently I have the Cary CD-308 running directly into a pair of BottleHead Paramour SET tub amps. Powering my Reference 3A MM DeCapos, this system sounds absolutely fantastic in my smallish listening room.
BTW, I borrowed a very high end pre-amp from a buddy this weekend while he's out of town. Adding the pre-amp did add a bit of dynamics to the sound, but I feel it lost a bit of inner detail. For me, it is not a good tradeoff. I'll leave my system pre-amp free and run the CDP directly into the amps.
Disclaimer: I do not often listen to Symphonic music or heavy rock. If I did, my opinion may be different.
Enjoy,
TIC