Perhaps drives larger than 160 GB attached to the Tempo Trio is dependent upon having a “primary” drive also resident on the ULTRA ATA connection?
AND having that firmware version 4.5.0 installed on
and with that (your 40 GB) drive in place, first? (Before installation of the Sonnet TT card.)
THEN install the Sonnet with the 160 GB drive attached… to then see if it would boot from that? (Still keeping the 40 GB drive in place.)
If this works, then you might try booting with that 40 GB HD removed afterwards.
And now I also wonder…
If you have an A (or a B) series Quicksilver motherboard in use?
820-1276-A or 820-1342-B