I’ve extensively researched the products available that meet your exact criteria. As for newer products, they are either on the small side (Zoom H4n, H6) without sync, (Tascam DP24/DP32) with sync. The Zoom R24 doesn’t have traditional midi sync, but it does have a very important function that the larger Tascams do not- time-stretch. For loop-based recording, this is a great feature (and allows the recorder to act as a pretty great device for capturing and editing sample loops), and allows you to then set the recorder to trigger and record the loops at specified points.

For Elektron Boxes (and other sequenced gear), this is a big plus- just record and trim your loops, then set where you want them in the recording without having to worry about punching them in at the exact spot. Also, the R24 is relatively small, and it (along with the H6) acts as an audio interface (meaning you could bring it in to the studio and throw the multi-track contents of the recorder into a DAW.

I’ve gone back and fourth on this many times, and the Tascams are simply too big and try to fit too much into the package. The smaller Zooms/Tascams are nice, but the Tascam DP008/Zoom R8 only make 16 bit recordings- so they’re out. The new Zoom H6 isn’t a portastudio (so it only has some basic FX/EQ/Mastering), is pretty small, and offers an incredible 96kHz/24bit .wav recording. It’s probably the best multi track recorder for the money- and can be expanded with the interchangeable top to add even more I/O.

If your goal is to hook up 4-6 different devices and jam out for an hour and record it, the H6 is probably your best bet. If you want to arrange/mix your recordings after, I’d go with with the R24.