I have several sets of phones that are single ended without any option to change to balanced cables. For this reason, I am definitely interested in Amp4 assuming it will be a single ended version of Amp3 with similar high current and high voltage.
I have been comparing the DX200 with Amp1 to both my home receiver headphone output and my AR-M2. So far, with about 80 hours of burn-in, the DX200 has a bit less bass than both the home receiver and the AR. I notice this mostly as a tonal balance issue. Specifically, the DX200 can produce equal bass to the other sources, but when it does, the highs are noticeably louder on the DX200 than on the other sources. This is with Sony MDR-7520 cans (see some amazing comments on these here:
https://pro.sony.com/bbsc/ssr/micro...ets-micro-proaudio-general-hearfrompros.shtml) and with Sony XBA-Z5 IEMs.
Also, so far, I would have to say that the sound of the AR-M2 is a bit smoother and more musical than the DX200. I believe the AR has the best and most powerful analog section of any DAP at the moment. It is the first DAP I found that sounded as good or better than other DAPs even when the others were playing through external dedicated headphone amps. On the other hand, the user interface on the DX-200 is far better. I am hoping that with Amp4, the DX200 will equal or surpass the AR.