Loved my xt910 too! Liking my Moto 5 also so far! And I am here because I too want an official Moto dock. Booooo.
But have you considered the following? It's what I've done in my car. And I have listened to decades worth of audio while I did other things. Get a little Bluetooth "audio receiver" from Amazon ($25 ish) and leave it connected by a 1/8th inch stereo plug audio cable to a line-in jack on your PC. Power it with as little as a USB 2.0 port. When you're ready to switch your listening from, say, phone speaker or Bluetooth headphones to computer speakers, just tap phone on the little "receiver" and thanks to NFC, the audio playback will switch over without a moment of interruption. It's seriously satisfying.
For bonus points, do like I did and take the little receiver case apart and throw the case away. Hot glue the circuit board, wire jacks, etc to the inside of something hollow and thin-walled like your computer case or for me, a plastic car dashboard panel. Position the NFC chip and antenna to match the intended tap area and again hot glue. I even sanded the plastic extra thin in one spot so the LED indicator of receiver (to show pairing mode etc.) would shine through the panel subtly. The wiring is all inside the dashboard and it feels exactly like the car was designed to have Bluetooth built in. I leave stereo on "aux" at all times so the stereo is silent until I tap phone on a certain spot of the dash and then whatever was most recently paused or is currently playing on my phone switches to the car system instantly. Then I just drop phone on passenger seat and drive.
Send tweet if you have any question. @duk3 This is one project I'm really happy with.