Is it my amp or my speakers?

I build speakers and amps. Recently I acquired the Purifi Audio EVAL1 power amp modules. These use the output modules used in the NAD 33 which is getting rave reviews. It is amazing how a great amp can make good speakers perform their best. Starke Sound has its AD4.320 on a "Black Friday" special. The best buy in power amps. It sounds as good as the Purifi unit and is a complete unit, ready to go out of the box. These amps have made every speaker I have connected them to sound wonderful. They are better than anything I ever built. They make my Golden Ear Triton 1s come alive. I'd say no speaker can do its best with a poor amp. If your Krell has preamp outputs, the Starke amp will amaze you. Emotiva has inexpensive preamps that sound fine if the Krell's preamps don't do the job for you..

I skipped over the other suggestions so if someone said this already please ignore this. $3k to spend. Used okay? If not you just cut your
performance in half. Know nothing of your CD player. I would buy a Cambridge Audio Integrated. Or a ChiFi Tube Integrated if you like that sound better. Upgrade the speakers to something pleasant sounding. So many choices. Assume you have $2k of the $3k left. Shop used Focal
as you like more forward sound. Borrow a better CD player somewhere
after you have the other gear. You will likely replace it too.

Finally had a chance to employ the very good advice and swapped out the amp to see if that was the problem. The only other amp I have is a Marantz AV receiver that’s been configured for 3.1 setup and a very different room dynamic, but I gave it a go anyway. The verdict: it *is* the amp. Even with the biases, the Marantz showed more detail than the Krell which, in comparison, sounded... muddy. So, now, I’m in the market for an amp: integrated, solid state, type A or A/B, not made in China, price <$3000. Any suggestions, please let me know. Otherwise, thanks again for the assistance.  P.S. I may still change out the speakers.

Audiophile rule #1: You will never find what's right for you by asking others what's right for them.

Find a way to listen to quality systems yourself until you get that aha moment. 

Krell in general is bright. Not shocked it is the amp.  At 25 years old, all sorts of things could be deteriorating including the caps in the power supply.  You could take the Krell in for a good refurbishing and that might solve your problem.  Alternatively, a new amp will work.  

Lots of choices.  If the Marantz sounded good, Marantz has a series of very good integrated amps that are modestly priced that will likely deliver on what you want/need.  

The new Marantz Model 30 is $2500.  Alternatively, a used PM 14s1 would be wonderful.  I would have to check if the Model 30 is made in China, the PM14s1 was made in Japan.  

If the Marantz was better but you still wanted more in terms of brightness, I would look at Musical Fidelity if made in Taiwan (not part of China, sort of) is Okay.  The M6si is a brilliant integrated amp.  

For made in the USA, the PS Audio Stellar Strata would likely be a good option and PS Audio will take your Krell as is on trade vs. it.  

I am sure there are others that will work wonderfully.  Good luck