The Zoom R24 has 24 different freely-assignable tracks (capability), they have an R16 that has 16 too. Most HDs seem to be in this 16-32 track range, depending on price.
Yes, you can hear other stuff (assuming you so so desire). It depends on what I am doing how I go about it, but let’s say one way or another I have ginned up most of a song with drums, bass, gtr, maybe some other stuff, and sort of mixed it togeher in Cubase. Now I am going to jam a lead gtr or maybe sing some vocals over it. Basically I will export the preliminary mix from Cubase to a .wav file, put it on the Zoom and assign it to a couple of tracks (since it’s a stereo file it goes on two “linked” tracks, one panned L the other R) lets say tracks 1 and 2. Then on track 3 I plug in the mic/instrument/whatever and play away to the accompanying music. When I feel I have it down, I hit REC and record what I am doing. I then copy ONLY TRACK 3 (that I just recorded) and dump it back into Cubase for editing/mixing with the rest of the already recorded tracks. If I have more to do, repeat. If I did cycle recordings, I’ll simply have more than one file to dump back in to Cubase - probably into lanes of a track.
It is basically EXACTLY LIKE recording it straight into Cubase - there is no conceptual difference. The up sides are that I don’t have to sit over by the computer, and don’t have to deal with drivers, latency issues, drop outs, etc. Which isn’t to say these are rampant issues if you go straight into the computer, but I never have to worry about it. Most HDs have a variety of features, in the case of the R24 it also doubles as an audio interface (if I did want to go straight into the computer for some reason) and a control surface (use the faders to control the mixer, etc). It also has a built in drum machine, which is semi-ok as a scratchpad, two built-in condenser mics (again, semi-ok for spur of the moment recording. And of course its got mic pre’s, phantom power, etc. It’s quite portable, so if you had to record something on site that’s awesome, or if you’re going on a trip and want to be able to jam (guitar, for example) the built-in effects while not epic are serviceable for this purpose. Some of the amp sounds are actually pretty decent (although I wouldn’t trade my Marshall in for it). The only thing some might consider a downside is that it’s max recording sample rate is something like 48 khz/24 bit. Eg, you’re not going to be able to record on it at 192khz. But I don’t see this as a problem since 44.1/24 bit is more than good enough.If you use it as an interface I believe it supports the higher sample rate throughput.
Mind you, this isn’t an add for the Zoom R24 - most of the available decent ones will do this stuff, with some variation. It’s mainly about how many tracks/inputs you feel you’ll need, and what other features are relevant/interesting to you (effects, built in drums, audio interface capability, etc). One thing I will say that I find very very useful is the fact that this one has a built in USB port for a thumb drive - which is awesome, because I don’t have to go plug the thing in every time I want to transfer files. Consider this strongly.