A few comments from a non-SC VI owner. However, I have owned Duntech Princess for 17 years so believe I can offer some relevant points; it's a Dunlavy family thing.
Room accommodation - some valuable points by the two responses above. Dunlavy took all measurements from a distance of 3 meters (rather than the standard 1 meter) for a very good reason. You must be at that distance for the drivers to integrate. John also recommended listening in an equilateral layout of speakers and sweet spot. Look at 10-12' per side for this set up.
The D'Appolito driver array provides wide dispersion so distance to side
walls becomes important. I believe this is why Dunlavy suggested long wall placement for both his Duntech and DAL speakers. I would say 3-4' from tweeter to side wall would be the minimum. Therefore, with 10' separation between L-R, your 17' width just makes the minimum. As Steve suggests, side wall damping will likely be necessary for best clarity and soundstaging.
Your room length offers full opportunity for adequate speaker placement away from the front wall while keeping all listeners out from the rear wall. The big problem with long wall speaker placement is the resulting listening seat proximity to the rear wall (opposite long wall). Yes, this can increase apparent bass response but it is not clean, accurate bass. And the SC VI should not need any bass boost.
Lastly, to optimize image placement, don't overlook vertical listening position. Your ears should be the same distance from the floor as the tweeters. A feature of the D'Appolito array is the vertical convergence of all drivers in each channel at the tweeter so placing your ears at this height is not only for high frequency tones but to hear the proper convergence of all the drivers. It is easy to understand listening at equal distances from L and R speakers, so think of the array in one channel turned 90 degrees on it's side to appreciate why this is important. If necessary, add spacers underneath your listening chair.
Power requirements - in my opinion, Dunlavy's designs are misleading in their efficiency ratings. My Princess are rated at 90 dB but with the experience of trying many different power rated amps, both tube and ss, this is not realistic. I believe a minimum of 200 WPC is needed and more is better. I would expect the SC VI to be similar. The problem is twofold. The first order crossovers in Dunlavy speakers are quite complex with many more components than other designs. Also, while I don't know about the impedance curve for the SC VI, the curve for my Princess drops below 3 ohms at two points along the curve, one in the critical bass range. After trying many other amps, including 300 WPC tube mono blocks, I've settled in with a pair of Halo JC-1s that are rated at 400 WPC into 8 ohms and 800 into 4 ohms. For the first time I feel I'm hearing what my speakers were designed to produce.
Duntech/DAL used values - a year ago a friend returned from the CES and came over to hear my system with the (then new) addition of the JC-1s. He brought the same test disc he made for CES auditions. After about 45 minutes of listening he said he heard nothing at the CES that bettered my system overall. A few select speakers/amps might have excelled in one area or another but nothing was better overall, and this included some costing $50-100K. At prices I've seen for Duntech/DAL speakers recently, I can't imagine a better value for anyone with adequate room and amp power/refinement.
One warning - John Dunlavy's designs are so revealing that you could end up needing to replace other components in your system, depending on what you own now.
Good luck in your decision.
