The Echo Indigo express cards are fantastic when run through external Hi Fi. They do 24/96 audio and you can really tell. They also provide a very loud signal out and a brilliant headphone output too. Not sure if they still make them though. Seen some on Ebay. (not cheap).

put old cpu back in. update to latest bios. put new cpu in and it should now work.
I did this exact swap on my t60 and had similar problems.

Try Fn+Spacebar with the mouse/pointer on the external screen.

Just done exactly this upgrade and had the same symptoms - until I upgraded the bios to the latest version after which it all started working.
And very nicely too.