Which speakers vs Vandersteen 3A sig's in large rm

Try a pair of Vandersteen subs and the matching crossover. It takes these speakers to another level not only in the bass but mids and highs too.

You seem to be describing a desire for Thiels. Other options include Green Moutain, Dunalvy and Meadowlark.

I second the 2WQ subs recommendation. In my room the 3As are extremely vivid/detailed and completely disappear with good recordings. They are very difficult to set up and need excellent components upstream. They will reveal any weak link. FWIW I struggled for quite a while with the 3A sigs and almost sold them. But once they are set up properly they are incredible. Even with the subs I think they still require a lot of quality power though. Good luck.