Have I got the wrong amp? or the wrong speakers?

Wow,push the pause button! There's so much that's not even being talked about or asked. I've heard some of the best gear ever sound like garbage AND some of the worst gear sound surprisingly good. It all comes down to how it's placed in the room AND if the room has any good possibility of decent interaction in sustating good performance.
Speakers are everything. And placement in the room can make or break the performance. The amp or receiver has a factor but it's nowhere as inportant as the first two.
Have you had other equipment (speakers) in this room setting before? What size is the room? If you clap your hands is the room have bright relections or is it dead?
The best speaker for one room may not be the best speaker for another. As an example; horn loaded speaker tend to work better in corners while wide dispersion speakers work best away from corners. Bass loading is often tuned by the distance from the walls or corners. Sometimes the distance or direction across the room can make or break the sound.
While your receiver isn't great, it has very little to do with the sound you are experiencing. Move your speakers around. try oputting them on stands. Maybe tyou have another pair of speaker to stack them on as stands.
There are RTA apps you can get for your phone as well as signal generators. If you have two phones, suggest putting the signal generartor through the system while viewing the RTA in the room for results. Compare it to what you HEAR.

Kudos to everyone's input. And to Larry's note, yeah. Doin' it since this stuff was made. And to the integrated amp: yes and no. There just as many bad integrateds as there are receivers. It depends on the brand, model and year it was made. I modify older pieces to do what they never did back in the day usually because there are now better parts and / or the designers back then weren't allowed the budget to do it right.

In any case one item that comes to mind here- try a BBE processor. Unlike an equallizer, it corrects time. It's a time correction equalizer that most any mid-end system can benefit. High end system don't need this as much because there are no (or few) time base problems to solve.
Most items in your system do not process all frequecies at the same rate of speed. Amps, cables,speakers, it all adds up. Even the room plays a part in this. Time arival equals clarity and usually flater smoother response.
I keep one on my own system (often in bypass) because audio recordings themselves have no standards in which they are recorded and often have time correction problems from the invironment and equipment where they were recorded.
Best of luck on the old gear. There's probably more to it than we know. Are the surrounds on the speakers dead? Are the pot on the amp cleaned, etc?