Upgrade an Old Setup.

[Kraken]

Well,

I've been looking around many forums and searching around on the Net a lot. We did a mini-upgrade to our system in early 2000's with buying speakers for our center channel to help boost the clarity of sound (pre-amped speakers). Now I'm trying to think of the next direction to go. We own a Sony SA-VA15 (hey don't knock it- it's done very well for all the years we've had it) which has a L & R tower with built in subs- L & R rears- then the center channel is two speakers (odd I know- but it works). NOW I have no receiver in this setup at all. I never knew how to introduce one to this setup since everything worked perfectly out the box and sounded great. But now I want more from my setup due to blu-ray.
The sound is purely running off the TV. The MAIN system (SA-VA15) does not support optical sadly.

So what do you think? Remember this is an upgrade or enhancement to the current setup with suggestions- I'm not going out to buy a new system. I don't have it in my budget at all.
Be nice- I know it's old- but be nice.

*side note- I'm having a bit of an issue with the subs. Since they are built in and HAVE to go where ever the towers go- I'm having bleeding prob. As in most of the sub bleeds into the next room (a lot) and I have had complaints from people next door (50+ feet away).
I was thinking of putting up padding on the wall in the next room to cut down the disturbance but am I losing a lot of my power (in the viewing room) since the bleeding is so bad.