Sorry this reply is very late in coming. I think the problem with remote control is down to the Sony-proprietory wiring of the headphone jack - the NW-ZX300 had the same issue. While the ZX500 now uses the Android operating system I think the 3.5mm audio jack is probably the same as that in the ZX-300, and it has 3 wires not 4, which most remotes (whether BT or a wired in-line remote control module) require to work with Android devices. So audio will pass through fine, but not remote operating functions. When I got my NW-ZX300 I bought a set of Bose QC20 (Android version) noise cancelling earphones after talking to a Sony support engineer on-line. (I already had the QC20 Apple version, which would only pass audio. The Android QC 20s didn't work, and it was after that I found out that the issue is the 3.5mm jack wiring.
The 3.5mm audio jack has 4 wires in a TRRS layout. This can be used for a separated ground output. Each channel has a dedicated Grd ( R+/R- and L+/L-) instead of the Common Grd in the normal 3 wire TRS configuration (R+/L+/R&L GRD) HiFiMan(and some other companies) supports the same TRRS separated Grd output.
The Sony DAPs, ZX, WM series, all have this TRRS capability on the 3.5mm. This provides a separate ground for each channel. This is not true balanced, but sounds better than just TRS. The Sony automatically detects the TRRS jack and switches to separated ground.
The normal 4 contact TRRS 3.5mm found on phones, uses TRS for audio, and uses the 4th contact for the microphone.
The Sony DAP (and most others) do not have a microphone. Only the older model (much older) DAPs had combined earphone remote controls. These were usually all in one, and proprietory. Some models implemented a short dongle with the microphone, and a female 3.5mm jack to plug a separate earphone into.
With todays market demands, there is no market for a wired dongle with remote, to plug into a DAP, and then plug a multiple $K IEM with special cables into this dongle, with unknown wiring and the extra complexity of an added circuit board and contacts, with the potential sound deterioration this could cause. Thus this capability is not built into DAPs. And it is highly doubtful that they ever will be.
Sony DAPs will only work with the small Sony remote. Why does it not work with a generic BT remote is a good question. Unfortunately, there is no answer....