Hi canumbra,
Welcome to the RWA forum!
Assuming you are using the balanced output (for apples to apples comparison to the Corvina), the Cassabria has an updated tube stage that has better top-end extension, and you can also roll-in tubes from the 12AX7 family.
I recommend you post on headfi.com, as we've done quite a few full-upgrades and most of the Corvina/Cassabria owners post there - but not all our customers post on these forums (shame!

).
Best regards,
Vinnie