Alright folks, It's been a few days now since I've updated my Xoom, so here's the process that I used. Note that it is different from the steps I listed in the original post:
Unlock the device via fastboot. Instructions here
. DO NOT RE-LOCK EVER!!
Flash the Official & complete US 3.0.1 HWI69 ROM. Links here
. Every time I tried to download the "does not require login" version from mediafire I got a corrupted zip, so instead I downloaded from the Motorola developer site (with instructions) here
Once the 3.0.1 Rom was up and running, and I had an internet connection, I got the OTA notification for the 3.1 update and installed it. It took about 10 minutes to notify me once I had connection, probably because it had to download it before notifying me. After the install and reboot process, I had a stock 3.1 install, but still didn't have sdcard access. So, I kept going.
Install CWM 220.127.116.11 recovery, using the fastboot method. Instructions here
Once CWM was installed and I had the ability to backup the rom, I immediately made a backup before EACH of the following steps was performed. I know it is overkill to make that many backups, but I wanted to be sure I wasn't going to screw up my device at any given step and have to start over again.
Root the 3.1 rom from here
. After rooting I had sdcard access within honeycomb at /sdcard/external.
Installed Tiamat 1.4.2 kernel. Instructions here
Installed the Language Pack from here
, but when I rebooted the system it went into a loop on the purple animated honeycomb logo. So, I rebooted into recovery again, and did a "wipe data / factory reset" - this allowed my machine to reboot normally, but I had to reconfigure all my settings and reinstall all my apps.
So as of right now I'm on 3.1 HMJ37, rooted, with CWM recovery, Tiamat kernel, and have international languages! It's great!!