In any case, this signal difference is not big, so we should not need a different amplifier chain for the two signals. The 20 dB of amplification in the BeatBox was a fine way, but not great in circuit layout.
The BBPD has an input referred current noise of 10 pA/rHz and a transimpedance of 2 kOhm, so an output voltage noise of 20 nV/rHz (into 50 Ohms). This would be matched by an Amp with NF = 26 dB, which is way worse than anything we could bur from mini-circuits, so we should definitely NOT use anything like the low-noise, low output power amps used currently (e.g. ZFL-1000LN....never, ever use these for anything). We should use a single ZHL-3A-S (G = 25 dB, NF < 6 dB, Max Out = 30 dBm) for each channel (and nothing else) before driving the cables over to the LSC rack into the aLIGO demod board. I just ordered two of these now.