I suspect what you may be experiencing is a matching problem. The yamaha doing a better job because of the higher output and hence increased headroom, which is the main peril when buying kit to work together. The Alumni's are pretty low efficiency wise at 86dB, giving a low powered amp such as the 1501 a lot more work to do, hence noise and distortion products will tend to increase.
Moving to a higher sensitivity speaker set (88db +) will aid to address this imbalance, and get the very best out of the 1501, or as you say the purchase of a higher powered avr. Which ever way you decide make sure you compare alongside the 1501, because technically it should see off most budget avr's sound quality wise with the right speakers.