1. Can you attach a HDD via USB?

I had mixed success with this. I installed a linux distro on the hdd, loaded the usb-storage module (and supporting modules), however the linux-arm kernel didn't like my particular usb-hdd hardware (I got some wierd USB errors). So I just hooked up ssh and used scp to copy the HDD down.

2. Can you replace the CD burner?

This is an interesting question. We know that the cd burning software has been "optimized" to support the specific cdrom drive. However, we also have the source to the cd burning software. It should be pretty easy to take a look at the differences between the stock cdrtools and the rio cdrtools. If the interface hasn't changed it should be fairly simple to drop in a new copy of cdrtools which would work with the new (and hopefully faster) cdrom drive.

The question would then be: is there anything in the player software that would cause the new cd burning program to die?

My 2c.