I am defeated in trying to answer this on two counts:
1. I am not scientifically changing one variable at a time;
2. I don't think I have the ear to accurately parse the impact of specific changes.
What I am trying to do, and having pretty good luck with, is follow guidance here on relatively economical changes to make in order to arrive at a very good quality audio setup. I am very happy with the results and haven't spent too much money. Good enough for me!
Yesterday I picked up and set up the Harman Kardon HK 3490, replacing the Sony bookshelf unit. I have a lot to learn about the 3490, but so far:
- noticeable improvement in the bass
- way more volume available, without distortion
- some additional separation and detail for instruments and voices, taking the Heresies up one more level it seems
I'm pretty sure I'm done for a while now. At some point I may look at adding a sub-woofer. But I feel really good about adding a pair of Heresy Is with new crossovers and caps and the HK 3490, all for less than $500. That's about the right level of investment for me right now.