As I said, I'm at the same crossroads as you. Your choice really comes down to your budget(doesn't it always). But this is how I see it.
The S6 or S8, paired with a C3 or C5 are the ideal speaker for your room size and for 2 channel. V2 or V3, doesn't matter. Obviously, V3 will have a higher output, but the V2's are more than adequate and the dealers will be looking to make deals to clear the inventory. Money no object: V3. I haven't auditioned the S6's, but I have listened to the S8 V2's and all I can say is you don't realize how hard you've been pushing those S1's until you hear the effortlessness of the S8's at higher volumes. It is simply unbelievable, pure, moving....you get the picture? One thing I know is that Paradigm is putting a lot of pressure on their dealers to limit the discounts off the V3's. 2 channel, sans sub, with either of those speakers would be awesome. With some decrement to 2 channel, and paired with a sub, the S4 would be a good choice for ht. Paradigm discontinued the S4, so their will likely be some great V2 deals to be had as the inventory clears. The S4 is a BIG bookshelf, but too small to be a floorstander, which is probably why it is discontinued now that the S6 exists. However, it's a good choice from a value perspective at this time. It's an excellent alternative to the S6 if you don't mind its odd size(I find it too big to be on a stand, but that is purely subjective) If you decide to go for another S1 or the S2, definitely get the V3 since you'll need every ounce of headroom you can get.
The S6 or S8, paired with a C3 or C5 are the ideal speaker for your room size and for 2 channel. V2 or V3, doesn't matter. Obviously, V3 will have a higher output, but the V2's are more than adequate and the dealers will be looking to make deals to clear the inventory. Money no object: V3. I haven't auditioned the S6's, but I have listened to the S8 V2's and all I can say is you don't realize how hard you've been pushing those S1's until you hear the effortlessness of the S8's at higher volumes. It is simply unbelievable, pure, moving....you get the picture? One thing I know is that Paradigm is putting a lot of pressure on their dealers to limit the discounts off the V3's. 2 channel, sans sub, with either of those speakers would be awesome. With some decrement to 2 channel, and paired with a sub, the S4 would be a good choice for ht. Paradigm discontinued the S4, so their will likely be some great V2 deals to be had as the inventory clears. The S4 is a BIG bookshelf, but too small to be a floorstander, which is probably why it is discontinued now that the S6 exists. However, it's a good choice from a value perspective at this time. It's an excellent alternative to the S6 if you don't mind its odd size(I find it too big to be on a stand, but that is purely subjective) If you decide to go for another S1 or the S2, definitely get the V3 since you'll need every ounce of headroom you can get.