you wrote in part;
::::I have no experience with it but the idea of a capacitor at this position... well.::::
awe.... spooked by a cap.... but consider... that in a series fed arrangement you will have a capacitor in the signal path (the last cap in your power supply is in the ac signal path)--- and likely that it will be much larger in value than the parafeed cap. So in either case you will have a capacitor in the signal path.
:::Is that FS100PS that Gianluca mentioned still available? I could not find much about it on the net.:::
The FS-100PF was a parallel feed output transformer.
MSL
Builder of MagneQuest™ & Peerless™ transformers since 1989
