You have a lot of other options like the Sr225i(analytical), DT880(comfortable, slightly warm), DT990(comfortable, brighter than the DT880), AT-A900(awesome bass & comfort), AD900(analytical, bass light), AD1000(analytical, bass light) just to give you a small idea. There are of course more detailed reviews available on TE as well as on head-fi.
The Hd600 sounds decent on the E17 but it doesn't make it really sing. The HD600/650 require a really good amp to make it sound as smooth and refined as it can sound. Otherwise you can get a HD600/650 now and upgrade your amp in the future. But you won't be doing it justice until you get a good amp for it. If you feel that you won't be doing that, then any of the above mentioned cans will do well with a HRT MS2 -> Fiio E17.
If bass and warmth is what you seek(although I don't blame ya cuz the HRT MS2 does sound treble happy at times to me), look at something like the AT-A900, HD650(with a good amp), D2k/D5k, DT880 in that order. Out of which A900, DT880 and Denons would do fine with your current rig but the Senns would require an amp.
Tbh I feel the E17 sounds better than any other portable amp I have tried. It may not have the best sound signature, but the dac section, build quality, the bass and treble control make it an amazing package.