Agree with Sidssp that it might be worth looking at the preamp as well. If you have a good dealer nearby who'll let you borrow another preamp to compare that might be worth trying.
That said, I heard the 3a Sigs a while back driven I think by Quicksilver amps. Relative to other speakers and systems I've heard (including my own) sounds especially in the mid/upper treble range were relatively subdued in the mix and came across as obscuring detail in that area. Although I haven't heard them (but very much want to) it seems this may have changed with models like the Treo and Quatro but could be wrong. Anyway, the Vandy's imaging and soundstage were outstanding so you might be a little underwhelmed in that area by a lot of other speakers. I'd try speakers like Joseph Audio and Reference 3A that also image well and may add a bit of detail you may be missing now. There are others but these are just a couple off the top of my head, and I've never heard the Tritons so can't provide any opinion there. Hope this helps and best of luck.
That said, I heard the 3a Sigs a while back driven I think by Quicksilver amps. Relative to other speakers and systems I've heard (including my own) sounds especially in the mid/upper treble range were relatively subdued in the mix and came across as obscuring detail in that area. Although I haven't heard them (but very much want to) it seems this may have changed with models like the Treo and Quatro but could be wrong. Anyway, the Vandy's imaging and soundstage were outstanding so you might be a little underwhelmed in that area by a lot of other speakers. I'd try speakers like Joseph Audio and Reference 3A that also image well and may add a bit of detail you may be missing now. There are others but these are just a couple off the top of my head, and I've never heard the Tritons so can't provide any opinion there. Hope this helps and best of luck.