Hi happy DX50 owners,
I'm new here, and I went over the whole thread (four days!). I'd like to share my two cents with you guys.
After playing with this little thing for several weeks, I have a feeling that the internal amp of the DX50 may not be that bad. It might be its DAC volume control that lowers down the resolution and dynamic range of the headphone out. I started to think about this when I pluged a pair of cheap Ety kids' (300 Ohms) into it, cranked the volume all the way up at low gain and found it sounded really good with a lot of details and good dynamics.
I normally listen at volume about 200 with my diy ciem. I tried to amp the LO with O2 at the same volume and did an AB test (kind of) by quickly swithing the IEM between DX50's HO and O2's and I could hear little difference (the bass could be a little better on O2 if I have to say). However, if I set volume at 255 while lower down O2's, it sounded much better to my ears (I can't AB them in this case though, so it could be just my imagination...).
I then used this DAP as an amp: just start it up without playing anything, and use its line out as a line in, it does work as an AMP only (CAUTION: try this at your own risk!!! It may damage the DAP and/or your ears). In this setup I AB'ed DX50 and O2; I could feel some difference but failed to tell them when blind.
Could anyone running it with an good amp please help me confirm this? Just set DX's volume at 200 or even lower and turn up the amp's; see if you loose any SQ. I suspect that a lower volume sacrifices dynamic range too much. If this is the case, I wonder if we can further lower the lowest gain so that the DAC can work at its full power. Two surface mount resistors may need to be changed and I don't think I can do this by myself...
The DX50 sounds good enough to me for portable use. At my desk, I also use it with a pair of Hafler TRM 8.1 monitors sometimes and the DX's LO volume control really helps!
BTW: I prefer the sound of 1.2.2 over 1.2.3beta. Simply better clarity.