I had the JL 1 sigs for about 3 years and the JL 3 sigs for about a year and a half,the difference is not subtle as a matter of fact it is huge.I have compared the CAT gear to everthing I could find Lamm,Aesthetix,Nagra,conrad jonhson,mark levinson and nothing beats the CAT stuff.I am using Avalon Diamond speakers and a Cat ultimate2 preamp.The difference between the JL3 mk1 and MK2 is the use of black gate caps and some other changes,I have not heard them but Ken said it is a worthy improvment over the JL3 mk1 and I have no reason to doubt him,he is usually pretty accurate.I would recommend the CAT gear for any application.