How much do caps matter-Cary SLI-80

Jupiter copper foil. Sonicraft sells them, and Jeff will give good advice for your application, but yes, they really do matter.

I recently replaced all four coupling caps in my SLI-80 F1 after one of the original Jensens failed.

There are lots of options out there but my recommendation would be to contact John at The Audio Connection in Seattle. He's a Cary dealer and very knowledgeable about upgrade and repair work on Cary gear.

He replaced all the caps in the amp including replacing the coupling caps with Cardas Golden Ratio capacitors. They're no longer produced but he has a substantial stock of them. His repair work is very reasonably priced, making it cost-effective to pay the shipping to get the amp to him.

And, yes, the Cardas caps did sound better than the Jensens, which were themselves an upgrade from the stock SLI-80 caps.

Changing your caps will change the sound of your amp. Consider if you want to alter your sound, and if so what type of change you’d like.

  
You have many options.

A bit late to the party pauly...

Yes, If you are going to ship or hire a tech, might as well replace all four IMO. I had those Jensen oils in my former SLI-80, they do produce a softer and more veiled over sound in that amp. If you like it, can always stick with it.

While I have the same caps in my Cary preamp now, doing some testing with a few friends who opted to go with the upgraded Mundorf's that Cary offers as an option. Any good tech can source the same caps as suggested above.I ran the Mundorfs in my prior Cary amps and current amps from another mfg. More open, clear, with nice texture. It varies. 

As others have said, each brand/type/model cap can all produce a different sound and result. Its worth figuring out what you'd like to change about the sound if you are going to replace all four caps.