The delay when switching songs is normal for Spotify and most other services like that. It's due to buffering, in order to reduce the effect of temporary network dropouts the music is buffered for a few sec, so quick dropouts don't result in the music dropping out, though longer ones can cause interruption. Was that way on my Playmaker, is that way on my Auralic Mini. When I'm playing songs off the internal hard drive of the Auralic though it responds instantly. It's buffered in the device doing the Spotify app, not in the Playmaker as far as I know.

You need something to get the IR signal into a closed cabinet. I've seen people use the little eye from a peephole like you use in your front door for this, put it in the cabinet door in front of where the equipment goes, though not a great solution if you want to keep the cabinet pristine. Fortunately the IR remote, like the Beo4, puts out a lot of power so maybe if there is a crack? Of course you also can set it to a fixed volume and control the volume from your iPad or such, though thats a tad cumbersome tome.

I don't remember how to do it now, but it's in the instructions. I seem to recall it took a certain series of button pushes on a Beo4 remote to move it into fixed output. I used it that way into the tape inputs of my Beosound 9000.

Plug one source into the aux inputs on the Playmaker, then plug the Playmaker into the BC2. The Playmaker will auto select its aux input when there's a signal there. Not sure if the streaming overrides the input or not, but if you stop streaming it'll pick the aux if there's a signal there. I ran the output of the phono preamp I use with my Beogram into the Playmaker that way and used it for a long time.