All three ARC preamps, the LS17, LS26 and REF3, sound like they are cut from the same cloth because they are.
The LS17 sounds very much like a smaller version of the LS26. The 26 has a bit more weight, extension, dynamic impact and resolves a few more layers of detail.
This same thing can be said of the comparison between the LS26 and the REF3, but the REF also has the additional benefit of sounding just a bit more liquid and effortless than the other two models, both of which use only solid state devices in their supplies.
I am an ARC dealer.