I also bought a new DSP board to be able to switch back and forth. The latest firmware (1.4) has more high-end detail, tighter bass, and a very slightly wider soundstage, consistent with what has been reported by others. But there is a certain fluidity that’s missing with the new firmware. Listening, for example, to "Dreams" by Fleetwood Mac, with the original firmware, Lindsey Buckingham’s guitar swells feel like they are completely enveloping you; with the new firmware, that feeling is gone, and the sound is a bit more analytical.
Some of whether you'll prefer the new firmware could depend on the rest of your system. I feel my speakers (Dali Epicon 6's) have a high degree of high-end resolution, which may be why the new firmware is not a slam-dunk for me.
I’m glad I can switch back and forth easily by putting in the other DSP module. This week, I’ve been listening with the original firmware. I like them both, although they are unmistakably different.