You can play all 8 plus a rhythm track back at once on the BR600.
Everything is complicated if you don't read the manual. I find even a little research helps with usability.
To double vocals you can either record twice, or record 2 tracks at once. The BR600 has pitch correction but I haven't used it (lies) it's pretty cool but takes some learning to get it right.
The drum machine buttons are also used to set functions, Pitch correction, panning, effect etc.
Editing isn't so hard. the concept is that you have 4 mono tracks, and 2 stereo tracks making 8 altogether. Then you have a further 8 V- tracks available in each of the 8 tracks making it 64. you can only play back one V-track (per track) at a time.
If you are going to be layering a lot I reckon it's best to record mono in tracks 1-4, then bounce to track 5/6 or 7/8 mixed and panned how you would like.
Your rhythm track is always separate until you bounce it to audio in one of the tracks.
What other gear do you have? I make use of mu GT8, and I take the phones out (which gives you all the pre amp, cab and mic sims) into the stereo in of the BR. Then I set it to have one pre amp left, and one right so I get that fat tone of having 2 amps panned hard in one recording take.
