Cardas Clear Speaker Cables?

Agree with @decooney except using JJ tubes 😎. Quite frankly, never used a JJ tube that I liked. They’re cheap and coupled with the fact that your amp needs a bunch of ‘em you’ll be tempted. I just replaced a set of reissue Mullard EL34 with Genalex KT 77 in an amp of mine and based on what I’m hearing they should do what you’re looking to do with your Classic 120’s. Whether it will be enough, only you can determine that. But it’s a good place to start and much cheaper than NOS Telefunken’s or Clear Speaker cables.  Oh, but definitely check first with CJ to be sure you can use KT 77’s.

+2 to what @marco1 said. I’m not a huge JJ fan either, the first set in my QS monos came out of the amps in a week and were returned to my local dealer for him to put in his stock for other customers to take advantage of.

Agree with simply contacting CJ directly, and posting a question on the CJownersforum about "which tubes to try in my 120 amp" to open and brighten things up a little more. Those guys over there can be helpful and many have tried it all. I leveraged the CJ forum quite a bit when I first started bouncing back and forth years back between TungSol KT150s and back to KT120s again for the type of sound I really wanted. imo, EL34s alone are a whole industry in itself within tube amp owners, lots of great choices and spinoff new-re-issue tubes like KT77s. Yes, lots of different tube stuff to try long before splurging on a set of Cardas Clear speaker cables for sure. I’m a 35+ year Cardas owner, tried most of them, and still a fan of Cardas [some, not all of their cables] but you’ve got some tube changes to try first, your Cygnus speaker cables might still be just fine. That’s all we are trying to say. Best of Luck.

@decooney - Thanks again for the advice. I really like the CJ Classic 120 with the EL34 amp. I'd set out for a warm and relaxing sound, but now realize our tastes evolve over time. In the future, when it's time to replace those Mullard EL34 tubes, I'll give the Ray's Tubes a go. 

@marco1 - You remember my quest?! Yes, I was looking for that older CJ warmish sound! I do enjoy it, but have come to understand some of the vitality of the music can get lost when you lose too much attack and incisiveness. Perhaps I am now looking for more of the modern CJ sound now? :-) 

I'm pretty sure the Classic 120 only takes EL34 tubes, but I'll do some research to confirm. Thank you for the suggestion. 

To @bluethinker one critical mention I noticed for you recently, fwiw.  Also ​​​supporting what ​@marco1 referred to you about re-issue KT77s. Its also discussed on the CJownersforum back in Nov 2019.  They get into the new company owners of CJ being in conservative "business mode" about only recommending the original re-issue Mullards" they reportedly designed the Classic 120 around, etc.  

The same thread and convo jumps into  "using other tubes" in the EL34 family very successfully in your amp. One mention about KT77s. If you truly want less of the warmth and more of the modern CJ sound now, here is the comment by one of the members over there about re-issue Genelex KT77s in your amp by (ajf75), quote:  "These tubes do give up a bit, but not all, of what makes EL34's so special (cozy warmth), but offer much better low end control, speed, and even a more extended/airy top end (but no high freq harshness IME).

Not to say the Ray tubes are not good, but they still may not give you enough of the modern sound you noted in your reply just above. It's possible the new GL KT77s might, and might be worth asking that member again on the CJ forum more directly. Try to acquire them from a known reseller with an established test & return policy guarantee if you try any other EL34 or KT77 tubes. I ran into a few bad tubes I had to return to a well-known reseller for refunds lately. I suspected poor packing and boxing as a culprit. 

I went from Cygnus speaker to clear beyond. It was a pretty huge jump

In realism and energy. Nothing at all wrong with Cygnus. They are great and very enjoyable.