Should I unzip the components first and then flash the image using fastboot, or is there another way? I'm wary of fastboot as I've already (temporarily) "bricked" the Xoom by flashing a zip instead of an image that way. None of the instructions I've read has much advice on getting round installation problems.
I'm guessing the persistent CWM was caused by my selecting (at an earlier stage) the CWM option to fix the problem of the stock recovery being reinstated at each reboot. Can this be undone? Although I've installed Xoom-Universal-Root, apps that require root access - including GooManager - also fail with an access error. It's hard to tell whether the device is now rooted or not, so if there's any method of getting further without root access, that would be great.
Edit: it looks as if the instructions I saw online, which mentioned two separate TWRP recoveries, were incorrect. To get Android Kitkat 4.4 onto my Xoom I didn't need the initial TWRP recovery, only the BigPart version. Once I skipped to the BigPart recovery, the problem described above did not recur.