Musical Fidelity A300 or Rega Mira 3 for Rock?

Greetings All -

Here's my situation and I really need some advice. I purchased the Cambridge Audio 640A integrated and matched it up with my existing Rega P5 turntable, Rega Exact cartridge, and Polk Audio RTi6 speakers about a 2 months ago.

I was immediately hit with how thin the setup sounded, so I ditched the RTi6's and replaced them with Polk's LSi-7s which resulted in much better bass response and way better high end control, although the bass is not very controlled and becomes "boomy" at times. I really can't go to floorstanding units in the room this is in - the wife would kill me!

I'm thinking this lack of control over the bass has to do with the amp not having enough power to deal with the 4ohm 88db LSi7s. I know the LSi7s are capable of dishing out very controlled and tight bass - I've heard them perform perfectly.

So, I've sold the 640A and the CIAudio VPP-1 phono stage I had with it and am now looking at a used Musical Fidelity A300 or a used Rega Mira 3; both of which have built in phono stages. The A300 concerns me a bit because I like controlled yet clear and crisp highs and I've read some things about the highs being rolled off to a degree on the A300 - although I've also read that after break in this isn't a problem. I can find almost nothing on the Mira 3 although I love my P5!

Let me know your thoughts on either of these amps and which would work best. Thanks!