OP:
The suggestion of a different amp was just to be different, not necessarily better. :) A romp through some classic tube amps might be a fun adventure, not necessarily a better destination.
For your budget and system I think overall keeping it as is and being careful to examine the subwoofer, speaker and room integration is what I'd recommend overall. For instance, look at the AM Acoustics room mode simulator for tips on where to not place your speakers and subwoofers and listening location.
Also, since these are non-destructive tests, try plugging your ports to see if the main speakers sound better from the mid bass on up. If so, you may want to adjust your subwoofer a bit to match the new, sealed speakers.
Otherwise I might recommend you listen to a pair of Fritz speakers, which have excellent performance, but not sure it would be a big improvement over what you have now overall.