I see you've posted this in a few forums, but the hd24 is fine with the mackie. In a way, designed for that desk and the similar behringer one of the day. These sent out tracks in blocks of 8. So most people if recording the vocal, on track 8, would hit record on track 16 which got fed the same source, the. You’d have two, simply. You could do the same on 24. Just the simplest way they worked. Of course, you're buying a technological antique. Finding drives is less easy though. The spec for drives wasnt wide.

The Alesis HD24 is the one to go for, but you should aim to find the HD24XR model that has the vastly better A-D and D-A converters in it. I had thought that finding suitable IDE disk drives would become a problem as SATA and then solid state drives became the norm, but it has not proved to be so.

There are several ways in which you could connect an HD24XR to your Mackie mixer, but the best would be to use the balanced Submaster/Tape Outputs to feed the inputs on the HD24, and then the HD24 outputs would be fed into the balanced Tape Returns on the mixer. You would need two 24-way TRS looms for this. Using Mix B facilities on the Mackie would give you full control of the record/playback track routing.

With an HD24, you can set individual tracks to record or replay, giving you the option of laying down (say) a stereo guide track, and then one or more artists recording their own takes onto blank tracks while listening to the guide track plus any other keeper tracks on headphones.

The review comments about the lack of "multiple track takes" probably refers to punch-ins on the HD24 overwriting the track underneath (as on a tape machine), and are therefore not reversible. However, as PaulEars mentioned, the HD24 has built-in input normalling, which means that initial recordings of 2, 4, 8 or 12 tracks can be replicated 12, 6, 3 or 2 times respectively to the remaining tracks up to 24. So if you were recording a 12-track take, in normalling mode this is sent both to tracks 1-12 and to 13-24, allowing you always to keep an original.

Standard HD24s are easy to find second-hand; HD24XRs less so, but they do come up. The main problem that manifests itself in older units is power supply failure, usually caused by the TOP227 switching device going short circuit. It's a custom power supply, but the switcher (and the fuse) is easily replaced by a competent engineer, so don't let it put you off.