Now I lost the track!
Paul, do you mean the design of the quickie is likely to be sensitive to hum, period, or that is better to use a low impedance amp with it to reduce hum (and so is better to use bigger teflon caps to hear their contribution even to bass frequencies)?
Sorry for the dumb question!
Hah - I'm sorry for the unclear post, so we're even :^)
For the best noise sensitivity, the coupling cap impedance should be less than the source impedance of the preamp (about 2K ohms for the stock Quickie, 4K with the PJCCS), at the lowest frequency of interest for noises. That places the "hot" interconnect line at the lowest possible impedance to ground, enabling it to minimize electric field (capacitive) coupling.
My usual rule is to make the cap impedance less than the source resistance at 120Hz. I also check that the response corner for the lowest rated load impedance is 5Hz or lower. These are two different and independent criteria, and are occasionally over-ridden by listening tests - I love science but it is not everything.