Power amplifiers usually have fixed gain, about 20x, or 26 dB. They need this to translate the input voltages (often around 1-2 V) to the speaker voltages.
They may have adjustment pots in the input, but the gain of the circuit itself is fixed.
Some amps, like Channel Island D200 are sold in two gain versions. As they explain in D200 manual:
"Gain: 32db (for use with VPC, PLC or other passive preamplifiers) or 26db (for use with active preamplifiers)"I would stay with lower gain if your preamp can deliver high enough level. Building up the gain in preamp should result in higher signal to noise ratio than doing the same in power amp (noisier environment). It also minimizes effect of noise pickup from ICs. Benchmark Media recommends lowest of three gain positions in my AHB2 amplifier. They stated that "Most power amplifiers have far too much gain, and this degrades noise performance of the overall system".
Utilize all of the sources gain don’t throw any away, is the best for the lowest noise, distortion and best sound.
If the source has enough gain direct to amp for the loudness you need, then you don’t need an active preamp with even more gain more noise and more distortion, a passive will be the best.
Quote from Nelson Pass