Crank,
I have the same setup as you. Just use a remote hack and there is no need for a firmware update. You can repeat the steps to get back the original setting. I grabbed this from a guy on some forum and it works beautifully. I have no expertise, so using the CD firmware upgrade would not work for me.
To make the Denon DVD-2910, 3910 and A1XV play DVDs from all regions:
1. Ensure there is no disc in the player.
2. Power off using the front panel On/Off button (not standby).
3. Press and hold Open/Close, Play and Skip Reverse (I<<).
4. Keep the above buttons held and Power-up the player using the On/Off button, holding the above buttons until the player's name disappears from the front panel.
5. Wait until the player finishes LOADING and the front panel of the player shows 0:00:00.
6. On the remote handset, press in sequence; 7 3 1 9 4 6 2 8
7. The unit should enter standby mode. On the front panel of the player, press the Standby button to turn the player back on.
8. To confirm the update, press on the front panel Stop and Skip Forward (>>I). The front panel should briefly display Region_A2. If not, then repeat the process 1-7 above.
This hack needs no firmware upgrade.
NOTE: I tried to play a region 4 DVD and had no picture on my panasonic. After researching, I discovered that you simply press stop, and then hit the NTSC/PAL button on your remote. It has something to do with it being a PAL DVD.