Yes. I just had a MOTU 896HD modded (including preamps) and also bought their external MicroClock.
The before and after is significant. The stereo image just jumps out at me after the mod. Much more detail and transparency.
The clock improved not only the MOTU but also a Behringer ADA8000 I use for tracking drums.
YMMV...
Matt, Jim and the rest of the crew were very helpful. When my unit arrived at BL. they dicovered one of the Firewire ports was non-functional. They definitely suggested not doing the mod with it like that. So, I got an RTA and BL shipped it to MOTU on their nickle. As soon as it arrived back to BL, they slipped it in and had it back to me quite quickly.
Thanks BL!