I have 2 working units I still mess around with.
Daxter Ice slim TA-085 V1
Piano black slim TA-085 V2
I got full NAND dumps, dumps of the IDStorage, keys, etc.
Cory's NandTool (nandTool 0.4 final NEO) is really good stuff
With software, I can dump Flash0 which contains the actual firmware files. These files are encrypted and sig-checked though.
Not sure how to specifically dump just the BIOS/Firmware.