If you've gotten accustomed to a smiley curve
by using your loudness control for years, you may have to 'un-learn' that way of listening. Fortunately, that is easy, just listen to a well calibrated system for extended time. Calibrating your system for ideal response is a little more difficult, and as Dr Mark said, may necessitate upgrades.
That being said, there is nothing wrong with enjoying a smiley curve on your music, although it may be a sin to dogmatic objectivists. Strictly speaking, it's not accurate, after all. It's ultimately your choice wheather or not to accept what statistics indicate you would likely enjoy, vs what your ears are telling you in real time (which, as mentioned above, may reflect personal preference, built in from prior exposure to music with a loudness curve rather than flat response). There is no right or wrong way to enjoy music. When the artist visits to berate you for distorting their art, I'll change my mind.
I feel for your situaiton. My first stereo receiver was a Yamaha which had variable loudness, which, from an amp safety perspective, was better than typical loudness controls because it cut the midrange rather than boosting the bass and treble; plus it was 'dial-a-smiley' over a range of midrange cut, rather than being one fixed setting on or off. I was very used to it, so much so that when I got gear that lacked it I ended up using outboard processors to regain the ability (primarily a BBE sonic maximizer, which does some other phasey things, but used it primarily to boost bass and treble frequencies when listening at low volumes to get the 'smiley' curve back). Since then I've gotten speakers which don't require eq'ing to sound properly phat, but I still have a Yamaha with the loudness feature in a bedroom, and still use the BBE for low grade bootlegs and such to spice them up.
It doesn't look like an outboard eq or processor is really an option given your receiver. Try what others have suggested (adjusting any onboard eq settings, audyssey).
[Oh, ****, just realized this thread is long dead, sorry for the bump!]