Too Much Gain the Issue ? (preamp and amp)

The input impedance of the Pass is too high for the SLP-05.

10K ohm is recommended (per a Stereophile review/measurements) and the Pass is 50K/100K depending upon single ended/balanced connection.

The mismatch will theoretically give a leaner sound (less bass).

DeKay

@avanti1960 I experience zero brightness, harshness or any type of sibilance issues with my XA30.8. I pair it with a Pass XP-12 preamp (9.3db total gain) using XLR cables.

Could be a combination of mismatched impedance exacerbated by too much gain. 

@Dekay

Based on the link below, you misread.  I quoteth:

The Cary preamp needs to be used with power amplifiers having input impedances of 10k ohms or greater if the bass is not to sound a little lean.

As you point out, the input impedance of 50k Ohms listed on the Pass site is more than enough.

I am so not a Pass fan, but what I have read from those I respect is that  these amps are very sensitive to speakers, and with the right speakers will sound full range.

I will say that when I repped InnerSound (ancient history) I took speakers to a dealer and for whatever reason the Pass with those transmission line speakers could not produce any bass at all.

Erik:

You are correct.

DeKay