So, had the opportunity to buy a set of Pioneer 6.75 woofs and surface mount tweets. The set is the Pioneer TS-D720C Premiere System ( http://tinyurl.com/6jplf8 ). To note: my deck is a Pioneer AVH-P5900 ( http://tinyurl.com/5jrp6c ).
I wanted to mount them on the center dash angled towards the glass so it bounces back to the compartment. The position I ended up with required I mill out the plastic underneath (a hidden part of the dash). Visually it didn't quite turn out the way I had envisioned . . . but at least it sounds awesome. FWIW, here are some pics.
The 6.75 speakers mounted in the doors with the enclosed adapter rings. BUT, they are so deep now my windows don't fully open. Like 3 inches of glass stays up. Damn it.
Think about it though. They are facing the "reflective" glass AND angled (or pointed) outwards. It actually separates very well. Sort of like having a pair of large surface tweeters mounted horizontally in front of the windshield.
I did the same thing on my Volvo a long time ago. It had a 6x7 speaker mounted smack in the middle of the dash. Popped it out and made a mount for a pair of tweets.
But the theory is easy to try out and test. I thought about getting the OEM pillar mounted tweets but decided it would be very unbalanced considering the position of the driver as seated to the left or right. You know, one speaker facing you and the other facing away from you.