I owned a No. 27 and a 27.5 and currently use a 23.5. I thought the 27.5 was an improvement over the 27, especially in the bass department. I upgraded to the 23.5 simply because my speakers benefit from the extra power. I think your money may be better spent on the older model amp which you should be able to find for under $2000 on the Audiogon.
Good luck!
Good luck!