Many reviews I’ve read of the Marantz PM14/15 have echoed your sentiment here; the top end is a bit rolled off, dark sounding, etc. Seems to me this characteristic is inherent to the amp and its design.
If you like the sound of your current Yamaha, why not take a look at the A-S1000, A-S2000, A-S1100 or the A-S2100 (whichever fits your budget)? They’ll have similar build quality to the Marantz and should give you more, in terms of sound quality, of what you already like about your current Yamaha.
I haven’t much experience with Cambridge Audio gear, so I can’t comment there.
If you like the sound of your current Yamaha, why not take a look at the A-S1000, A-S2000, A-S1100 or the A-S2100 (whichever fits your budget)? They’ll have similar build quality to the Marantz and should give you more, in terms of sound quality, of what you already like about your current Yamaha.
I haven’t much experience with Cambridge Audio gear, so I can’t comment there.