If you end up recording with a rack mount interface enough eventually you'll run into the problem of needing more simultaneous analog input channels. Typically you'd be limited by the number of available analog inputs on your base unit. But many units come with ADAT digital expansion for the inclusion of additional A-D converters. Those converters would also need to be fed an analog signal. So you can either buy a converter set and then buy preamps to feed it. Or you can go for something like the Digimax FS.
The Digimax FS is 8 preamps with inserts on each channel in a 1 rack unit space combined with 8 channels of A-D AND D-A conversion via ADAT i/o, with 8 channels of direct, pre conversion analog outputs as well as 8 post conversion analog outputs. Wordclock is handled via BNC cable and there is a word clock termination button for when the D-max happens to be the last unit in the distribution chain. In short, it's a very useful channel expansion unit.
I've used the Digimax FS as the primary channel expansion for my Firestudio 2626 via ADAT. Hook up is simple and problem free. It's just a matter of attaching the right cables, pressing the right buttons and you're good to go. What makes the Digimax so good are it's ins and outs. With a Digimax you can run 8 additional channels into your ADAT equipped interface and you can have each channel take advantage of signal processing via it's insert. You can also run the pre-converted analog channels to wherever you wish, be it a recorder or a cue mix system for direct monitoring, while you run the converted signals to your main interface. You can also monitor the return signals through the post D-A analog outputs. All of this makes for a very powerful, flexible channel expansion unit.
The sound of the preamps on the Digimax is fine with me. It's not special and it's not bad. It's just basic. The preamps don't have quite as much headroom as they would need to handle quiet sources with gain hungry mics. But they do fine in the vast majority of recording situations. If there is ever a need the Digimax has 6 line inputs and two instrument DIs.
All in all I recommend the Digimax FS for it's connectivity and abundant usefulness and a sound that doesn't kill your recordings.
I've had this unit for a few years, I had originally bought it as an analog front end for an M-Audio Delta 1010, but recently started using the ADAT in/out with my Focusrite Saffire Pro 40. Here's my impressions:
Compared with the preamps on the Focusrite, I'd say these are in the same territory, though maybe a bit more sterile sounding. They seem unexcting, and don't seem to flatter much. I get my best out of them by not running them too hot, and on signals that aren't begging for mojo. Don't run the pres too hot -- they get noisy on the last couple gain settings.
Compared to my GAP Pre-73 or BLA B12A, they seem very boring. I can get much more fun and mix-ready tracks out of those pres for most things. But, I've still never had any issue getting useable and useful tracks out of them. I typically reserve them for my additional drum tracks and they do fine in that purpose for the price.
The conversion quality seems respectable for the price at this level. Again, on par with the Focusrite interface, and useable. Next to my nice conversion, it is lacking on low and high end. So I would much prefer the nice stuff on the main money tracks in a mix, but for the extra tracks, it works fine in the mix.
Also, the insert jacks are a nice touch for outboard.
Overall a decent expansion box for a modest setup if you need more tracks of utility to add to an ADAT in. With the prices these go for used, you could add 8 i/o to yor setup rather cheaply these days.