Generally Eros wants 2mV, maybe 1.5mV minimum. Below that the tube noise becomes obtrusive. Personally I think it performs best at 3 to 5mV input, which would be a 10:1 stepup - not as much as the 4722; the 15095 at 150:15K would be closer. That will buy you one or two clicks on the FP-III control.
The high sensitivity of the DX4s, plus the relatively high gain of the FP-III, are probably the root of your problem. Without doing the detailed numbers, I'd reduce both Foreplay and Paraglow gain. Foreplay III is easy - check the manual for input sensitivity adjustment. Is the Foreplay Extended?
You can put shorting plugs into one input of the Foreplay and listen; if you hear too much tube rush, or more hum than the Paraglows alone (with shorting plugs in their inputs), then an attenuator at the Paraglow input will help further. Check my "signals and Noise" paper on the Community page if you have the time and patience.