Good luck with the ET3SE, Glenn. You're wise to stick with the Bryston for now because you may be pleased with the combo as is. Also as the previous poster remarked, if the unit is new you will find that the preamp's sound will change as the caps form. At least that's what I found with my Premier 140 when I had the upgrade done. Although, I felt that the initial sound was about 80% to 85% there straight from c-j after they made the modification.
I have used the O-rings that c-j supplies but never really heard any difference. They should in theory help with tubes that are a little microphonic. This was how I ran the tubes in my 16LS2:
Regards,