The Marantz is warmer, and slightly smoother, but it does have some bass problem that has been discussed over at the HiRez Asylum. I think Dan Wright is modding the HDRAM analog output sections to deal with that. Reference Audiomods has a mod (about $1100) where they completely replace the analog section with transformers.
The Sony is slightly drier, but more detailed and and greater impact because it doesn't have the Marantz bass issue. SACDmods.com offers a mod to the 775 for about $325. I'll bet that really turns that machine into a killer.
I could easily live with either machine unmodded. Both are very clean and musical. Differences between the two are not great, unless you're really into minor differences, and even then I would not automatically assume you would find the Marantz better. However, don't get me wrong, the Marantz is a great machine, and it would be my choice if I had to choose between the two, which I'll probably have to do eventually.
All my comments here and in my last post relate to redbook. I've been so fascinated with the redbook performance of both machines, I haven't been too interested in buying SACD discs and trying them out. My SACD disc collection stands at a grand total of 2 (1 for each player I guess).
At this point, who knows about the future of SACD. I bought both machines to play with SACD, but found the redbook performance of both machines so good, I'm considering selling my current reference front end and having either the Sony or Marantz modded to use as my redbook source. Eventually, I make take a more serious look at SACD, but right now I'm looking at both machines as very good CD players, that just happen to have SACD and MC capabilities. I'm not set up for MC, so that's not a consideration for me.