Man KEW I'm going through an existential crises about this upgrade. I'm over thinking it I think way too much as the time gets closer I've about talked myself out of the ultra's and I don't even know what I'm trying to talk myself into. I put a thread on it over in the loudspeaker section I seriously think I'm tripping
Trust me, I can relate! I can obsess over this stuff to the point of becoming walking dead!
Well, I think the Ultras are a great step up from the Primes and your allegiance to SVS is understandable.
This hits on one of the big questions of Audioholics and upgrades!
Every now and then we have someone who knows nothing about audio who has $20,000 for a system. For a situation like that, I really like the idea of buying a pair of good speakers (say the $1,000/pr. Ultra bookshelf speakers) to listen to and later use as surrounds. - Two reasons:
First, I worry if he immediately goes out and listens to speakers, he might not choose the speaker he would like most if had the experience of listening to good speakers first. IOW, refining the ear and learning what is important to him as regards sound quality.
Second, it seems a shame to only have the excitement of a big upgrade once instead of spreading it out over two or three upgrades.
Your Primes are pretty good speakers and you have spent some time listening carefully and tuning your system, so you are in pretty good shape.
However, IMHO, the Ultra's are among the least expensive speakers that do
nothing obviously wrong. For example, I might have a hunch that they are a little bright from listening to them (which is not a terrible thing), but without a better pair of speakers in the room, I do not have conviction of it.
This is purely my subjective opinion, but I think if you bought a pair of Ultras, and listened to them long enough to become very familiar with the sound of your favorite music on them, you would be in a pretty good place to recognize the speakers that "creme your twinkie" when you hear them!
With your subs, the Ultra Bookshelves would work fine for refining your ear. They are good dynamic speakers and if you might want to use them as surrounds later, they give you an inexpensive way to accomplish this. I also like bookshelves in this role because you can take them to someone else's home and compare without the production of moving towers. A local shop let me bring my AVR and Paradigm S-2's into their shop and compare them to their S-4 (which didn't offer an improvement to my ear) and the Focal Electra 1028Be (which sounded better, but at $6,000/pr I wasn't sure it was worth it). This led me to the Focal Solo6 Be which has the same drivers and seemed to offer most of the same advantages as the 1028 Be.
I have not heard the Primes. By reputation I understand them to be good speakers. However, people who have upgraded from the Primes to the Ultras were not disappointed.
Please understand, my intent is to offer my best advice. I am definitely overstepping here, as YMMV quite a bit. For me, with what I know now, this is how I would approach it.