really 8
well, i see you are learning the MR-8.
It really is an 8 track system. 5/6 and 7/8 are dedicated stereo tracks, that are hard panned. I record a lot of stuff stereo, like drums, guitar, and vocals, so i just record the stereo source onto the stereo channels, with no problems.
you can also do as mentioned above, and record onto 1-4 and digitally copy into the other tracks. or you can use the bounce features.
two things you need to remember
NEVER try and record from INPUT B only. if you are recording one track, you have to use input a
you can NOT record 5 (of 5/6) and then try and record 6 later. they have to be recorded together. you cant record 7, or 8 alone either. it has to be in it's pair.
with that small limitation, and understanding digital editing, you can work around almost anything to get your tracks into the MR-8
good luck