So far I have tried a USB stick, a Linux storage gadget, and 2 micro SD cards. Both the USB and emulated storage device booted to the logo then a black screen where the fan spun down then sat there for 3 hours before I tried something else. The weird thing about both the micro sd’s is that after booting them once the deck no longer recognises them as bootable drives. I have to reflash the recovery image before I can boot to it again. One of the cards (cheap nameless 16 gig) booted to the logo and sat there for several hours and the other (1TB Sandisk) booted to the logo then a black screen and is still sitting here 2 hours later.

Edit: leaving the 1TB overnight got as far as the touchpads vibrating when touched.