Actually, the LO inputs to the IQ boards have AP1053 (Cougar) amps on them. These are 10 dB amps and so putting 10 dBm in puts us on the very maximum of the LO range at 20 dBm.
I think the distribution box levels are fine.
I'm not sure I agree with your conversions, BUT:
The IQ boards use a PE4140, fancy MOSFET array as the mixer, and according to Peregrine (manufacturer), they can be operated with 0-20 dBm LO drive. I'm not recommending we drive them at 0 dBm, but perhaps the numbers you mentioned are OK.
The Rich demod box wants 10dBm for the local oscillator inputs, so I measured the values that we have coming out of the distribution box. I'm using the "Spare 55MHz" and the "POP11" outputs, both of which had terminators so were not in use.
The 55MHz had ~600mV peak, so between 5 and 6 dBm.
The 11MHz had ~800mV peak, so about 8 dBm.
This is not enough dBm for either. Going in search of RF amplifiers now...