At the risk of being insultingly obvious, I will offer a different opinion ...
Before you start exploring the option of replacing either the receiver or speakers, play with some items that are free or inexpensive, such as:
* Speaker location/positioning/stands - even modest changes may make significant improvements in the quality of sound. Before moving the speakers/sub, move yourself around the room. Would a different seating position help? Toe in or straighten the speakers, pull them out from the wall a bit, rotate the sub 180 degrees, etc. Put your speakers on makeshift stands - the level of the tweeter relative to your ears is extremely important for some speakers.
* Chair. This is a big deal for HT as some chairs have backs that effectively block side/rear speakers. The back should be well under ear level. No, this isn't necessarily free or inexpensive, but you may find that swapping furniture from elsewhere in your home takes care of it.
* Room enhancement - tame room reflectivity problems. There are some very reasonable DIY designs out there. To get a sense for what may help, try hanging a blanket behind the speakers, behind your listening position, at the reflection points, and on the floor. Not that this is a good long term solution or even a great test, but it may help you determine if it's an area worth exploring. You may find that simply placing curtains over windows, placing a bookcase (with books) in the room, or adding an area rug helps a lot.
* Wires/cables. No, I'm not a "spend $1000 per cable" kind of guy at all (heck, I don't even spend $100 per cable - I use mid-range AR interconnects and Soundking speaker wire), but look at all of your wires/cables to see if there are any blatantly weak points, like 22 gauge speaker wires. Moving from crappy 22 gauge wires to crappy 12 gauge wire would make a noticeable improvement (especially in bass) for next to nothing.
* Power. Again, not a "spend $5K on a filter/regulator" kind of guy, but you may be getting some low level interference that could be easily removed with inexpensive (under $300) filtering. I have a *very* low level hum that I only notice when doing night-time listening to music with lots of silent passages (classical, jazz) that I am trying to figure out. If I can't eliminate it at the source, I will start exploring more elaborate power filtering than what my current inexpensive surge protectors offer.
Hope this helps. If you are insulted, get over it.
Cheers,
Bill
