I haven't compared the LS6 vs the LS9, it may just be a "more is better" thing with the 9's. If the LS6 is a better fit in the room (or budget) they are both cut from the same cloth so to speak

I have lived with the LS9 and now have the Super V installed. My system is quite high end and my 21d x 14'6"w x 9'h room is treated sounding good. That said, the LS9 was still a little big for my room. The sound however was mind blowing, best I've ever had.
I decided to move to the Super V for tuneability, reasonable size and the ability to play with other types of amps (SET's and the like). The Super V is most likely the last speaker I will own for the next few years. I am smitten

. The bass is deeper than the LS9 and hits just as hard. Voices are so realistic (size and tonality) that you need to look no further there. Adjustability of the sub bass on the V is a huge plus too. The big 2" tweeter will make you think the "high hat" is in the room with you I'm not kidding.
The only place the big LS and the Ephipany speakers can beat the Super V is massed strings, chorale voices and room ambience. The Neos (with sonicaps & JPS wire) are the best I have heard at that. The Neo3's in the Ephipany 20/21's are the best I have ever heard way up top. You can pick out every single voice in a 100 voice chorale in its own space. Shocked many of friend with that trick.
All in all, both are an amazing value, and the differences are smaller than you might imagine. The 9's are a tough DIY build (and crushed a few small companies that have tried) but they reward your effort. The Super V is just top on my "fun factor" list. However, you still need 3' behind them.
I have sold 3 great loudspeaker systems because they were too big for my room. Wiser now