Proac 2.5 Response tweeter upgrade with Ribbon Tweeter?

No idea on the matching, but I owned a pair of 2.5 and now own the D40r with ribbon tweeter. Much better speaker.

"more 'body' to the sound and deeper bass"

It looks like you are using a tube amp with medium to low power. The Proac 2.5 is very inefficient, but can produce deep bass (see the review in Stereophile). You should borrow if possible a fairly powerful solid state amp (high damping factor and 100-200 wpc)  to see how that works with your speakers.

Glad you like the Tannoy speakers. I am sure they are a much better match for your amplifiers.

 "The sound stage is huge and 3D (compared to my Proac 2.5 and the D48r's) "

If you don't have a huge 3d soundstage with the D48r something else is wrong