Is it my amp or my speakers?

Having too few reflections can be a problem too. :)  If you get close and it sounds better, you may need some partially reflecting panels, or perhaps more bass.

See how they sound very close up.  If they still sound lifeless, yeah, get new speakers.

Speakers.

The amp is 25 years old and the speakers are 8 1/2 years old. The amp/speaker match should be ok. Has this combo always sounded this way or is this something recent? Before you start spending money, try to pinpoint the problem. Try someone else’s amp in your system or try your amp in someone else’s system. Or borrow an amp from your local dealer. The Krell is a nice integrated but they wear out like anything else. The bottom line is we don't know if the issue is with your amp or your speakers, but you should find out before you spend your money.

I had Tekton Lore reference speakers. I was at a tipping point, as I’d initially heard Tektons with a tube amp...but had always favored solid state. Moving to/investing in a quality tube rig was just not in the budget, nor doable with our house setup (needed to keep things simple) plus I’d gotten a really decent solid state integrated. I sold my Tektons and got some Totems - which I think are better for me and sound so great with my amp - and never looked back. Point being, pairing is a big deal. As stated above, try and try your Tektons with other amps (tubes and solid state) and your Krell with other speakers if possible. Now wish I had tried mine with tubes and/or could have kept those Tektons...better to exhaust a good portion of that curiosity with trial and error. 

I think it could be your speaker wires and interconnects. If you go to OCC single Crystal copper you will hear a big difference. Cuz all your other equipment looks pretty good.