Well. The receiver is probably worth ~$75 now on the used market.
That might give you a vague idea. Mid-fi home theater equipment from the mid to late 90s doesn't tend to retain value well.
That said, you can probably have a lot of fun with it regardless of the low value.
You have some decent power in that receiver. Pro-logic only though, I believe.
The dvd-cd player is old as far as dvd players go. 1998/9 I think. If it still works well, this might be one of the best finds of the group.
I probably would resell the cd changer. Use the dvd player to play cds.
Frankly, I hope you didn't pay more than $500 for the whole lot. That might even be generous. You can get much more state of the art than that for $500 off agon or ebay. Even new, $500 goes a long way toward starting a "decent" ht rig these days. Anyway, HT / Stereo is a fun hobby. Welcome to the madness.