Upgrade amp or speakers?

I concur with your findings on the preamp. The difference between a decent preamp (Classe in your case) and a good preamp (ARC in your case) is so much. If I were you I would get the new preamp, let it settle in the system for a few months and let the ears acclimate to the new sound. After that I would re-evaludate the system. You may want to continue upgrading the preamp at that point, or you may want to get a different amp. But changing more than one component at a time usually results in suboptimal result.

Thanks all for the responses. I am presently auditioning an ARC SD135 amp and an ARC LS17 pre with my gear and here is what I have found so far. I did a mix and match with it all starting with the LS17 and my Classe CA100. What a difference. The music really came out of the MLs with clarity and definition. Then I went back to my gear with the Classee CA100 and CP35 pre to really see the difference. The music was muffled and music passages seem to just blend all together. To think we have been listening to this for years! Next I did my pre with the SD135 and the music was still muffled and not detailed, so determined my pre has got to go! I hooked the SD135 with the LS17 and maybe it was my anticipation and "expectations" with what i was imagining I would be hearing out of my MLs but it was a let down to say the least. We have a few CDs that we use to audition gear and in one song the words coming from the speakers were making my wifes teeth hurt. It seemed to have either really cleared up the song but it was too much "ssssss" in the words and in some of the cymbals. The clarity just didn't seem as good as with the Classe amp. But i think the biggest downfall, and it probably is personal, is the sound of the cooling fan of the amp. Though the literature says it is a quiet fan, it was like sitting next to my refer. In those nice quiet passages of certain songs, the fan overtook the room. I don't have a large music room so it could be sitting that close really is a disadvantage but after an afternoon and eve of it, we could not take it. I also expected a lil more "umph" from it but it really didn't have that until we really turned up the volume, which is very little of our listening. So the adventure continues for an amp but I really think the LS17 is a really nice piece of gear. It could be that I just might keep the pre with my original amp, I have read that mixing an SS amp with a tube pre really brings out the music, I can say it is but with the MLs, I am thinking that there is an amp out there that will just take us to music bliss with this new LS17. Would like to see what you all think of this all. thanks!! Happy Listening.

Unless you are in love with the electrostatic sound, you might consider a quality pair of moving coil speakers and stay with your electronics. You might use a variety of footers to "tune" the sound of the system from there until you hit the sound you are looking for. I have had great results from a combination of Black Diamond Racing puck/cones and heavy brass Mapleshade footers.

I would definately sell the Martin Logans and keep the amp. A friend of mine owned Martin Logans and he much prefered the sound of my large efficient horn loaded speakers. Also these are the type of speakers (very revealing & efficient) that sound good with the slightly warm sound of Classe.

This is a question that no one else can answer. If you are ENTIRELY happy with the speakers then you can change the amp, the sound will probably be different but there is no guarantee you will like it better. The speakers will make much more difference so if you are even considering changing them you should start there. Very often tuning the system with suspension devices, new cables or room sound treatments will make more difference than changing out amplification or sometimes even speakers. Remember that components of equal high quality may sound quite different and until you identify in your own mind exactly the qualities you value most you will be on a never ending search.