isn't it annoying to ask you this question every few days can i stop this worming?
means the phone required to reboot every few days in my case. lol rough metaphor in short: wire vs BT apt-x vs BT audio = cd vs mp3 vs fm (IMO) bad n4 do not support apt-X. else bluetooth would be the best solution (esp with sennheiser mm450x).
get of the volume warning is to flash a custom ROM. If your volume is typically full, then you wouldn't have seen it. It's only when raising the volume from low that this warning pops up. if this is a default android option or it's from CM/AOKP/PA custom rom (as I'm using PAC rom at the moment): settings > sound > down at the bottom, uncheck "Safe headset volume"
If you're referring to the impedance of the headphones, most people would be using 16 or 32 ohm drivers which would match the phone just fine, but that point isn't as significant as the fact that some material we want to listen to might be recorded at too low a level.Since we're talking about Bluetooth, my experience is that Nexus 4 android phone or nexus 7
Using a MP3 source on your phone with a headset connected via cable and referring to it as "CD"? Unless you're really a high audiophile and in a real quiet room I doubt that you can hear the difference between "normal" bt audio and bt apt-x. And besides: apt-x is a proprietary audio codec. That's why it isn't supported by N4 by default. If you want it to be supported, try to get a kernel with a BT stack that supports it.And I believe you don't even try BT audio because you think that the quality doesn't meet your "standard" because the N4 doesn't support a proprietary audio codec (and for that I already gave you a possible solution). BTW: There have already been given solutions to your problem. But unfortunately they are not applicable if you're on stock ROM.