Conrad Johnson vs. Audio Research - Sonic Comparison Impressions

The older CJ equipment would fall into the warmer/lusher-sounding equipment.  I once heard a pair of CS 3.5s like yours driven by a CJ Premier amplifier (I think it was the Premier 3 or 4, a big stereo unit) that made the Thiels sound absolutely gorgeous in the midrange and highs, but it lacked some control in the bass that you could only get from a solid state amp.  At the time I opted for a Krell KSA 80, mainly because I was switching from Thiel CS3s to Duntech Princesses, but had I been staying with the Thiels I would have opted for the tubed amplifier, it sounded so beautiful with them. 

The ARC house sound has always stressed high resolution, and many of their products have been more neutral (early ones, like the hybrid M300s, VT  hybrid series and Classic 60 and 150s) could be characterized as comparatively dry-sounding).  Over the years the CJ house sound has, from the few times I've heard it, become more neutral, though never quite as neutral as those earlier hybrid ARC designs, and ARC's designs have become a little warmer, but not at the expense of resolution.

Personally, if I had to make the choice now I'd lean towards the old CJ, can't get that one audition out of my head., but finding one of those (and in good shape) would be difficult  A more recent ARC like a VT 200 might work well with the Thiels as well.  I think a VAC amplifier like the Phi 200 might also be something you should consider (I own one and like it a lot), it has a very nice midrange and excellent bass control.