Your A/B/C/D-in-your-home idea is terrific and the best (only?) way to really evaluate gear IMHO.
With all I said above, the Thiel CS1.6's are hard to knock, very accurate but a little bass shy. Often however, honesty in music reproduction can get in the way of enjoyment and involvement, and a hump here or a dip there in the grequency response actually sounds more "musical" in many rooms and to many ears. The difference between theory and practice I guess...
I would prioritize your search this way:
Spendor S8
ProAc Studio 140
ProAc Response 2.5 (Bass King, tonal champs, but will never disappear in the room)
ProAc Response D15
I don't know anything about the Spendor S9.
The Thiels would either fall at the top or the bottom of this group, depending on your personal tastes. Given that you feel your current pair of Thiels are underpowered, probably towards the bottom with your existing set up. Just one person's opinion.
With all I said above, the Thiel CS1.6's are hard to knock, very accurate but a little bass shy. Often however, honesty in music reproduction can get in the way of enjoyment and involvement, and a hump here or a dip there in the grequency response actually sounds more "musical" in many rooms and to many ears. The difference between theory and practice I guess...
I would prioritize your search this way:
Spendor S8
ProAc Studio 140
ProAc Response 2.5 (Bass King, tonal champs, but will never disappear in the room)
ProAc Response D15
I don't know anything about the Spendor S9.
The Thiels would either fall at the top or the bottom of this group, depending on your personal tastes. Given that you feel your current pair of Thiels are underpowered, probably towards the bottom with your existing set up. Just one person's opinion.