Thanks for sharing the pics of your installation in the crack Jamie! I'm thrilled to hear that you're hearing good things out of the RTI's. What's the total combination of coupling caps you've got in each channel now?
My RTI's did indeed arrive and are now in place in my mainline, singing sweetly! As depicted, they're a little too large to sit down between the C4S boards and output transformers, where the stock coupling caps previously sat, so I ended up mounting them just above/overhanging the c4s boards. They are "anchored" via adhesive zip tie mounts stuck to the outer metal edge of the output transformers. I'll have to keep an eye out to see whether the adhesive really holds over time, but the caps are actually supporting their own weight via fat, rigid leads.
The sound is supposed to change quite a bit over the next few hundred hours, but my sense is that the mainline, with the RTI's, already sounds a tiny bit more transparent than stock, with slightly increased micro-dynamics and possibly even cleaner transients. From the limited articles I've read on the subject (e.g. http://www.reliablecapacitors.com/pickcap.htm ) this seems consistent with teflon caps' ultra low dielectric absorption and dissipation factor. I'm definitely looking forward to seeing how they mature with burn in and will make a point of reporting back on that. The mainline is so good stock, that I certainly wouldn't suggest this is a necessary upgrade, but these are clearly outstanding, ideally spec'd coupling caps for the mainline, if any of you are so inclined!