If you enjoyed your LS-15 and want the same sound signature, but (a lot) more of it, the LS-26 is a wonderful amp.
Personally, I like the synergy of CJ amps and preamps together. If you can find one, the CT-6 is the unsung hero of the CJ preamp lineup - it's like getting 90% of the sound from a CT-5 for less than 1/2 the price. The CJ pre that sounds most like the ARC gear IMHO is the PFR. I know that you want tubes, but it's a great preamp and is available for a very reasonable (aka cheap) price.
Personally, I like the synergy of CJ amps and preamps together. If you can find one, the CT-6 is the unsung hero of the CJ preamp lineup - it's like getting 90% of the sound from a CT-5 for less than 1/2 the price. The CJ pre that sounds most like the ARC gear IMHO is the PFR. I know that you want tubes, but it's a great preamp and is available for a very reasonable (aka cheap) price.