What System addition made you realize a problem

I'm dealing with an expensive whopper now. Picking the best 6M XLR cable between my Wavestream pre-amp and Lamm 2.1 amps. The Wavestream and Lamm's show up the short comings in my previous cables. So far the cables I've demo'd are in the $6K to $12K" deal" range. I've brought up all my components to SOTA levels and my long time Alpha-Core micro-pearl just don't live up to the total potential now.
My friend is currently using Jena Labs cables (Pathfinder, I believe is the model), between his ARC Ref. 3 and his Lamm M2.2s. (By the way, is your amp the M2.1s or the ML2.1s?) He used to use Nordost Valhalla cables before that. (And before that, he used to use the Nordost Quattro Fil cable, which by the way, is what I use between my Ayre K-1xe and my Lamm M2.1s.)

He says that he thinks the Jena Labs cables are (slightly) more musical, but that the Valhallas are (slightly) more detailed. (Six of one, half a dozen of the other, I guess.)

Hope this gives you some ideas. Good Luck!

PS All the cables listed are, or were, balanced cables.
transparent reference-MM2 (just below opus), calibrated for your preamp's output impedence and your amp's input impedence. do NOT get OPUS- in my opinion they're only slightly better.
i was really surprised by the degree of improvement i heard over transparent reference (w/xl technology, no "MM"). i am the last person to promote cables as i assume they are basically a rip-off to begin with. plus i usually don't "hear" (or perhaps it's "appreciate") subtle differences between component A and component B. but if there's a remarkable difference that makes virtually every piece of music i put on more enjoyable, i am happy to tell other people about it.
i got them thru the trsp. upgrade "program" so i saved some money, got brand new cables, and supported my local dealer all at the same time. but even then, they were still ridiculously expensive. oh, that's right, now i have to upgrade again from MM-1 to MM-2 tech...
I keep touting this cable til I am blue in the face (with little response) however...

try Audio Note AV-VZ - the supelatives do not exist to describe the qualities they impart (or do not impart) to the sound of your hi fi