Thanks for posting. I hope you don't mind if I offer a couple of comments? In answer to your questions...
1. There have been breech risers and spacers available, most notably from JRA, but these products have not been available recently (you'll see other posts on this further down this Forum). One reason I chose the "screw in" offset approach with the QB79 Paintball Adapter was that it's very easy to install. I didn't go with the riser breech or spacer approach as then the factory front band will no longer fit. Replacement hammer and cocking pins may required also. Either a new front band would then need to be designed and made, or the barrel and main tube no longer support each other with (I believe) detrimental effects on accuracy. All these would add to the cost of the "fix" to provide increased clearance between 9-ounce tank and barrel.
2. If you're not too happy with the 2-stage trigger setting, you can adjust the pull weight and overtravel screws in the trigger mechanism. I'll also send you a PDF of the adjustment instructions so that you can investigate further. The trigger does smooth out significantly with a little use.
3. The XP Tune Kit bolt uses a thin probe to push the pellet into the barrel. This increases the muzzle velocity by reducing the barriers to gas flow behind the pellet. The narrow probe bears on the center of the pellet as it pushes it into the barrel. The standard bolt probe bears on the edge of the pellet - this may make loading pellets easier, but it significantly reduces muzzle velocity. Typically, I find it easiest to thumb the pellet into the rear of the barrel and then push it home by closing the bolt. Some pellets will load more readily than others.
I hope this helps. Please email me at email@example.com if you would like me to call and discuss.
Archer Airguns Inc.
Online stores http://www.archerairguns.com