I have read over in the AVS forum several users having problems that are using HDMI>DVI. I have HDMI all the way for my A1 and the upgrade took about 40 minutes. I tried NIN this morning and it seemed to fix some of the stop points it was having with the DTHD during some of the songs.
Yes, I see a few posts there that 2.1 gives slightly faster load times, some report slightly better PQ, and several reporting that disks that gave them glitches now play fine. But it's a flood of folks with a DVI connection that have the problems I have. When you startup an HD DVD or DVD, you get the "splash screen" that says Toshiba HD DVD, then nothing. You have to "break" the HDMI>DVI connection by powering off your display, wait for the player's LED to display "No HDMI link" then "stop". Then power back up and hit Play. The screen flashes for a few seconds while it negotiates a new HDCP handshake, then you get the display of the movie.
I played around with it last night using that trick. Yeah, slightly faster load time, it seems like a slightly more clear & sharp PQ. The only disk that ever gave me a problem was Happy Feet, when it locked up at the dreaded 28:50 spot. Last night it just hung up at that point for a few seconds, and then kept playing. But the DVI connection problems way outweigh the slight improvements for me. I'm going back to 2.0.
When I posted that you can not revert back, I was relying on two Toshiba Support reps telling me you cannot revert, probably a stock answer. Also, with no picture on my display, all I could see was the player's LED saying "version up" & nothing happening. I tried my FW 2.0 disk from Toshiba last night again, using component connection to my display. (The Setup and other menus display as a garbled mess on my HDMI>DVI connection, and the power off/on trick doesn't work because the display is not protected content, so it doesn't try to negotiate a new HDCP handshake).
On component now I can see the display saying "Proceed Anyway?", with buttons for "Yes" or "No". Two have posted on AVS that they were able to revert back to 2.0 using the disk, with no problems. I'll wait for a few more brave souls to confirm this before I try it.
I remain very happy with my XA1, and full committed to HD DVD. I appreciate Toshiba's best efforts to make their players more fully backward compatible with the older DVI standard. But FW 2.1 clearly needed more compatibility testing for DVI before it was released.