The situation you explain sounds preposterous. If a director demands that no actor be miced, but still wants amplification then the method you go about describing is very ineffective. The director cannot get it both ways - either he/she lives with the reality of actors in
microphone or lives with the reality of an un-amplified performance.
You could use boundary and hanging mic's - though I do not think the
efficacy of these types of microphones is worthwhile in most settings (that isn't to say they aren't useful tools to help amplification, I just personally find that in most settings directors want miracles out of these tools)
The series receiver/transmitter you were using is a
Sennheiser ew - but what series (G1, G2, G3?) and what type of
microphone were you using (ie
Sennheiser MKE2, Countryman B3,
etc.)
Of note: One mic will not cause
feedback with another mic.
Feedback is a loop created when a
microphone is picking up its own sound from a
speaker. This loop will keep on attempting to amplify itself - creating
feedback.
