I own a pair of JL-3 signatures and owned ARC amps for a number of years before. My favorite ARC amp was the VT130. It had a lush midrange warmth and an exceptional 3-dimensional quality. But it was a bit weak in the lowest frequencies. I did compare this to the VT100 MK I when it came out. The VT100 had a more neutral tonal balance, more extended low end but did not at all have the midrange magic of the VT130. Both were comparable in terms of resolution and noise level. There were no other significant differences than the ones I have noted. As I understand, the VT200 is a beefier version of the VT100 so I suspect a similar comparison would exist between the VT200 and the VT130. The question here would be: is the output transformer in the VT100 the same as that in the VT200? If so, I suspect the VT200 would not fair very well with demanding speaker loads any more than the lower powered ARC amps.
The VT130 ran out of steam with Magnepan 3.x speakers but it was a soft clipping. Still its 110w output rating played the Magnepans fairly well to moderate levels. When I tried a pair of Classic 150 amps, there was only a marginal increase in power drive capability, but the CL150's were just way too analytical and fatiguing. And when they clipped (150w monos) their annoying protection shutoff circuit would kick in. They were not a good fit with the Magnepans at all.
Moving fast forward through a Counterpoint NPS400 and Wolcott mono amps, both of which worked very well with the Magnepans, I now own the JL-3 Signatures. I also now use Soundlab A1 speakers, but I was able to play with the JL-3s with the Magnepan 3.5s for a week until I sold the Maggies.
The JL-3s are in a completely different league than the ARC amps. They are rated at 150w but this is far different than the CL150 150w rating. Where the CL150's pooped out at moderate volume levels, the CATs played the Maggies with no strain. I was so impressed by this after all the hassle I had with the CL150's giving out so early. The CAT designs' strengths have much to do with their massive output transformers.
Concerning sonic differences, the first thing to note is resolution. The Wolcott was ahead of the VT130 here, but the CAT takes this much much further. You hear more lower level details in the recording than ever before. We read this claim often, but here it is quite significant.
A more impressive strength of the CAT is that it has a dynamic contrast ability that my past amps did not at all have. When I compared the ARC amps with the Counterpoint, and later the Counterpoint to the Wolcotts, I never noticed such a difference here so if there was one, it was subtle. It's really incredible to hear the CAT start softer and then build up to explosive levels. This is NOT subtle at all.
Another huge difference is how the CAT handles the attack on the notes of accoustic instruments and piano. This has to be heard to be believed. I never heard this quality like this before until I first heard it in the JL-2. Simply amazing.
One thing the CATs do not have is a peak in the midrnage to give it an added warmth like so many other tube amps. For years I really liked this quaility in amps if it was not excessive, but once I heard the neutrality and dynamics of the CAT, I now have no wanting for the warmth.
Btw, the JL-2 is one heck of an impressive amp, and what a great value. This amp will probably drive all but a handful of difficult speakers that would be better served by the JL-3s. The qualities I described above are common to both a JL-2 I heard in December and my JL-3 signatures.
There is one issue with CAT amps. If you do not have a dedicated circuit for your amp now, you will need one for the CAT JL-2. When these things are powered on, they take quite a huge surge in power. With the JL-3s, I had each amp on its dedicated 12 gauge 20A circuit. The breaker would trip the first 1-2 times when I powered on an amp. This was a pain so I contacted Ken Stevens who wrote back that same day to tell me one 30A ciruit would work for the 2 amps provided I turned on the second amp about 5 seconds after the first but not a lot later as the first amp would be running with a lot of steady state current....and thus the powering of the 2nd amp would trip the breaker. Since I already had two new 20 circuits, the wire was changed to 10 gauge, the 20A breakers switched to 30A breakers and now all problems are gone. I made sure these two 30A circuits AND the circuit to drive the rest of the audio system were put on the same phase. Ken wrote that this was important.
I'm not convinced that you need a CAT preamp to get the best out of their amp. I have heard the CAT preamps over the years vs. what I have owned and they were impressive indeed. But I would not rate them as being in an exclusive club of a few. I can tell you that the CAT amps are indeed at the top. Perhaps the new Legend preamp will be a perfect match for the amps. But the JL-3s sing quite nicely driven by my BAT 31SE and Aesthetix Io components.
Hope this all helps.