Sorry it took me so long to respond...
APT CSVT, it was the basket part that was hitting the sides of the openings. And only 2 screws could be put in on a given speaker end because of the length. I would have had to drill new holes any way I looked at it.
As for the depth, I didn't look that closely as I was focusing on the other part not fitting, but I think the depth WITH a spacer would be ok, since wjang said he has the Kappa's with spacers, and they are deeper than the Pioneer's.
BTW, I ended up exchanging the 6x9's for the Pioneer plate speakers (P682 i think). Those will be going in tonight when I get home.