i tink class-a amps *do* sound more powerful than comparably-rated non-class-a amps - prolly because they put out more current. the proacs would definitely like more power, tho what ya got should be sufficient in a smaller room.
the least expensive way for you to increase the power would be to get another matching classe amp & bi-wire - put the biggest amp on the mid-woofs of the proac; or if ya got another classe 70, ewe could try biamping vertically.
proac uses the audio research ls-16 & ls-25 preamp w/the a-r 100.2 amps, fwiw....
doug
ps - i have an electrocompaniet aw100 amp f/s on audiogon - class-a, 100wpc into 8 ohms, 190 into 4 ohm, >80amps current output... :>)