Many moons ago, I owned the 2.3s. My friend also worked at the high end shop and for about a 6 year period, I did virtually all of his deliveries and set-ups with him, including many pairs of Thiels.
I had decided to upgrade the 2.3s. The store where my friend worked had limited floor space and they just had the 7.2s. So on an out-of-town business trip to Northern California, I stopped at a Thiel dealer who carried all the models and they were very gracious and let me listen to all of them. I spent most of the time with the 6s and 7.2s (I had set-up and delivered many pairs of 2.3s). I decided on the 7.2s.
When th 2.4s cames out, I delivered a bunch of those. Personally (and much of course depends on your room, listening preferences and electronics), I'd go for the 2.4s vs. the 6s. Yes it (the 6s) is older technology. If someone listened almost exclusively to classical, depending on the other factors, it might be something to consider.
