I've used a DA-7 on a couple projects (a while back) and I recall that it sounded quite good and it was easy to operate. It's still owned by one of my best friends and he still loves it.
Still, I feel the need to defend the DM-24 here. After much research, I bought a DM-24 ~2 years ago and I'm very happy with it. I also considered the Yamaha 01V96 and the Ramsa DA-7. The Yamaha didn't offer the flexibility and abundance of I/O I needed and I was concerned about the Ramsa having been discontinued.
DM-24 Pros:
1) Extremely flexible routing (best in class, IMO)
2) 3 option slots for significant expandability; many Tascam option cards available
3) Affordable (even more so now)
4) A/D Converters are quite good, pres are fine for most work
5) Flexible monitoring matrix
6) Powerful headphone output (x2)
7) 2 x S/PDIF & 2 x AES/EBU I/O built in (note: only 2 of the total 4 can be used at once) and built-in ADAT I/O (8 channels)
8) Mine has been reliable -- no issues, no surprises
9) Generally sounds great
10) Tascam Forums is a great resource:
http://www.tascamforums.com/
DM-24 Cons:
1) OS can take a while to learn
2) Flexible routing can mean complex routing sometimes
3) DAW control is hit or miss -- works better for some DAWs than others
4) A/D and D/A for sends, returns and monitor output are not as good as input channel A/D (I've got the parts list if you're interested). I added an external D/A for monitoring and it made a big difference.
5) Some users who leave their mixers on 24x7 have had LCD screen issues
6) 96KHz operation effectively halves the system's I/O. I believe the Yamaha has the same limitation, but I think the Ramsa can run at 96KHz with full I/O available. I'd confirm this before purchasing any of them if 96KHz operation is important to you (download the manuals). Otherwise, you could be in for an unpleasant surprise....
If I had it to do over, I'd look more closely at the Yamaha primarily on account of their recent purchase of Steinberg and improved integration with Cubase (Yamaha Studio Connections). I don't regret the DM-24 purchase, especially since I'm mixing ITB more and more these days and the DM-24 is the best digital router around.
Note for RAMSA and DM-24: the meter bridge is an extremely useful option, almost necessary for mixing. I wouldn't want to use either unit without one. FYI, I don't believe Yamaha offers a meter bridge for the 01V96.
-Synth80s