There's nothing wrong with equipment of the past... especially if it continues to work well day after day. And if it sounds great, I'd definitely keep it. Also, I have a great deal of respect for audio companies of the past years; as they have well built products / built with proper materials (unlike consumer products today; even yamaha has started to use thin plastic enclosures or chipboard-LDF for enclosures).
Of course, Modernization - and trying out some new equipment is a joy and IF it sounds just as good and saves space, and gives you better compatibility and ambience - at a reasonable cost$... then it can be a fit for you.
I'll give you a few suggestions that may or may not work - but at least it is an educated guess at what will work best. The 2 sets of speakers that I'll name are Professional Studio Monitors: the type that DJ, recording studios use for their "sound reference".
These speakers are suppose to produce FLAT response to most of the audible frequency, and uses the latest cutting edge technologies to obtain this.
1. KRK Rokit 5 or Rokit 6
2. M-Audio BX5a Deluxe
There are others, but these are the 2 that are reasonably priced at well under $400 for the pair.
They are a 2.0 system that can be hooked up to your Polk Sub or KRK makes their sub too... but* they go down to about 50hz +-2db -and their power is rated at about 70watts RMS... so unless you are a basshead, there's no need to use a separate subwoofer [it is nice to know that you can hook them up though].
I've listened to the Rokit 5 but not the Bx5a's yet, but I've heard that they are equals. They both use carbon fiber derivatives [Rokit: Glass Aramid, Bx5a: Kevlar] for Woofers and Silk Dome tweeters in a Waveguide. Both also use Thick MDF cabinets.
The Rokit series use 4 internal amplifiers [1 per driver] ... so they do not need any receivers or amplifiers to take up space.
They have XLR connectors or regular RCA / Headphone jack analog connectors - so they'll connect to anything including ipod/mp3 players, DVD/CD/Bluray players, PS3 systems, TV's... etc.
These speakers can be found on Amazon.com or Guitar/ Music stores.
Email me if you have any questions:)
Happy Listening, and Good Luck!