To Plossl or to XL?

Rob,
I have a Discovery 12.5 truss dob and an Astrosystems truss 16" dob.I believe the pentax units work quite well and my pentax 10.5 does not ghost on Jupiter in either scope. You may also wish to try the university optics orthos or the ultima plossls which have good contrast and little or no ghosting. I read posts from other amateurs claiming their Radians do ghost on bright planets.

I've been using two televue plossls in an 8" f/6 dob and they work very well, (within their 50 degree field of view). The 15 mm gives an exceptionally strong tonal range on the moon. I used the 10.5 with a 1.5x barlow to find the trapezium stars a through f. The limitations are field of view and eye relief.
This is not to suggest that the pentax XL's do not work well, I simply haven't used any.

Rob,
I have tried televue plossls in both of my dobs and I find them to be of high quality without significant ghosting issues. I am not sure of the reason for poor quality images in your scope unless seeing conditions in your area are poor or your optics are not collimated properly. I would recommend a laser collimator made by Howie Glatter. His laser costs about 100.00 for the 1.25" model but it is highly accurate and it will withstand being dropped on the ground without being de-collimated. I have found the lasers provided by Discovery to be un-collimated as have other amateurs. I returned one to Discovery and their replacement laser was even worse.