vandersteen 3a signature or thiel 2.4 or 2.3

Given what you are currently using the Vandersteens would be the more forgiving choice. The Thiels are excellent but quite demanding of everything else in the system, you'd be on a forced upgrade path where the Vandys will sound very good at all kinds of in-between stages.

With all due respect to the other posters I think your gear will do fine with the Thiels. I think the Thiels more immediate sound will come closer to replicating the sound where most live jazz is heard, i.e. jazz clubs. I think the Vandersteens are fussier with regard to placement. The Thiels fussier regarding associated equipment, especially amps. Again, I think your gear will do fine. The Thiels are a bit more forward and crisp, the Vandersteens more laid back and rich. The Thiels probably have less depth but more definition in the bass region and visa versa the Vandersteens. I find plucked bass better on the Thiels and bowed bass better on the Vandersteens. The Thiels have a more forward and extended top end, something that bothers some people, the Vandersteens a sweeter top end, that to some may lack that last degree of transparency. IMHO since your gear isn't an issue, it's just a matter of room and taste. Both are truly excellent products. If you are drwan to these you might also want to consider Dunlavy or Green Mountain. Good luck.

The more I think about it the more I think your gear might be better suited to Thiels than Vandersteens. You might want to also add Meadowlark to the list.