I don't have experience with the 6.1s or the c3, but I'm going to throw in my 2¢ anyways. 
First of all, I also have heard nothing but great things about the 6.1s, the C3 (and R3s for that matter). I owned the 4.1s with the 4.2c and the 4.2rs, and I hoped to one day upgrade to 6.1s, C3 and R3s. Instead, I couldn't pass up the Cyber Monday sale on the EMP Impression line especially with my love for RBH. But I digress....
The 4.1s and Swans in general, sound fantastic musically. I can only imagine how much better the 6.1s would have sounded. My biggest issue was the 4.1s didn't timbre up with the 4.2c as well as I'd hoped. The 6.1s and the C3 should timbre up nicely. Coincidentally, I didn't notice a huge difference between the 4.1s and the 4.2rs, so I'm guessing as long as you go with high-quality in-ceiling speakers for your surrounds, you shouldn't notice a huge difference. But, please don't take my word for it. I'm sure there is someone here with far more experience than I, and can guide you to towards purchasing specific surrounds that will match up nicely.
Another issue with the 4.1 line is the mounting piece for the tweeter atop the tower. It's a little difficult to explain, but the piece of plastic that holds the tweeter in place looks a little cheap and stuck on. The 4.2 line improved this and has a nicer mounting piece that is smooth, streamlined and just looks like it belongs a little more. That said, Swans are incredibly beautiful speakers and this really is nitpicking. Just thought I'd throw it out there.
Finally, I'm believe Swans have decent resale value in general. I posted mine on Craigslist, got 5 offers the first day, demoed the speakers once and promptly sold them to that guy for more than I paid for the set in the first place. YMMV, however. Best of luck to ya! :T
First of all, I also have heard nothing but great things about the 6.1s, the C3 (and R3s for that matter). I owned the 4.1s with the 4.2c and the 4.2rs, and I hoped to one day upgrade to 6.1s, C3 and R3s. Instead, I couldn't pass up the Cyber Monday sale on the EMP Impression line especially with my love for RBH. But I digress....The 4.1s and Swans in general, sound fantastic musically. I can only imagine how much better the 6.1s would have sounded. My biggest issue was the 4.1s didn't timbre up with the 4.2c as well as I'd hoped. The 6.1s and the C3 should timbre up nicely. Coincidentally, I didn't notice a huge difference between the 4.1s and the 4.2rs, so I'm guessing as long as you go with high-quality in-ceiling speakers for your surrounds, you shouldn't notice a huge difference. But, please don't take my word for it. I'm sure there is someone here with far more experience than I, and can guide you to towards purchasing specific surrounds that will match up nicely.
Another issue with the 4.1 line is the mounting piece for the tweeter atop the tower. It's a little difficult to explain, but the piece of plastic that holds the tweeter in place looks a little cheap and stuck on. The 4.2 line improved this and has a nicer mounting piece that is smooth, streamlined and just looks like it belongs a little more. That said, Swans are incredibly beautiful speakers and this really is nitpicking. Just thought I'd throw it out there.
Finally, I'm believe Swans have decent resale value in general. I posted mine on Craigslist, got 5 offers the first day, demoed the speakers once and promptly sold them to that guy for more than I paid for the set in the first place. YMMV, however. Best of luck to ya! :T
