rom flashing - Updating HTC Sensation to Ice Cream Sandwich is stuck in a boot loop

I'm trying to update my unbranded HTC Sensation to an Ice Cream Sandwich stock ROM (from here).

I've followed the various instructions where I install the ROM, then flash the phone with the HTC Sensation firmware from here, which matches my phone's CID.

The phone is now stuck in a boot loop, but I can't find any help out there for why it's doing this. Could anyone suggest an answer?