I have always liked the products and service Solo has provided and have had your stuff on 3 different cars now.
The kit you made for the Mustang was by far the best of many I tried. The way you routed the exhaust over the axle provided a lot more clearance and was so much better than other set ups (stainless works for example sucked). That car sounded bad ass and got lots of complements.
Getting back to the G8 I think there is still one area that you might be able to offer another alternative. Lots of guys start off not intending to do much in the way of mods but want a little more sound. Those guys typically get the axle back and love it.
Then then Mod bug bites them and they start doing more to the car. Before long they have LT headers with no cats and suddenly that axle back that sounded so good is now WAY to loud.
I know that you have the mid mufflers that can be sold seperately, and thats how I solved the issue with my first G8 (don't think you had the any of the other systems out yet) Anyway, my point the majority of the guys in this situation are off loading the axle backs or adding a Magnaflow mid muffler.
If you had an alternative solution, that would allow customers to keep the existing axle back, yet mate it to a new mid section that woud be a nice way to be able to do things in stages. This would be great for the guys who didn't have the cash at the time or the forsight to see the end game. Perhaps also a short 5" round x 9" long muffler that could be spliced in right behing the tips on an existing solo axle back or even an entirely new axle back that has a mufflers and the J pipes built in? Either way it might be a way to keep guys from looking at other brands.
For me (if money was no option) I would love to ditch the entire system I have frankensteined together from other parts laying around. I would just go with a Solo 3" set up. It would be a pain though because I would have to cut the flanges off the headers (required welding to mate up to a custom mid section of random parts i have) additonaly starting over would be costly. It's hard to fork over the cash and ditch what I already have. The point though, it puts me in the same place a lot of guys eventually end up (I'm assuming it will, I'm not done with the project) asking the following questions.
How do I quiet down the Solo axle backs once I get headers? If I can't, what do I need to replace them with? There should be an answer to that question with the Solo name in it, that is priced at or below the cost of what guys pay to fab up some max flows or vt mufflers. IMO if you could do that you will have another product that could be near the top of your poll results in short order!
Oh, and if you ever need a guinea pig count me in!