Yah, all of the wireless models have their own amp. Even the last gen of rs 170,180. They have to have an amplifier of their own to produce a signal to send to the headphones.
But an amplifier only outputs the signal that is inputted, but increased.
So, if you were to use a headphone amp to alter the signal, that adjusted headphone amplified signal, would go into the sennheiser base amp, and travel to your ears intact.
It is when you use the effects on the base (which are software presets in the DSP), that you may get crappy sound. And that is because your headphone amp would be coloring the tone of the music, and so would the sennheiser base, so some frequencies could be muffled, or distorted.
So, you can use a headphone amp, but you need to be careful of using too many processing effects and messing up the tone.
You also have to be careful (really in general of all sources, not just headphone amps) of the output level of the source. Too much gain (volume) will cause distortion, but worse overdrive the internal amp of the Sennhiser and cause it to burn out prematurely. Using appropriate, good sounding levels, that don't clip and distort will be fine. It's common sense. But it's the same of you were connecting a radio, or a TV, and turning it to max volume into the poor little Sennhiser amp and overloading it. Obviously, that would be bad, so don't do that with a headphone amp either.
But, yep you could use a headphone amp. Chances are, it would output analog though, so it would plug into the minijack in of the rs base.
I'd recommend rounding up all of your optical outs on your sources, running them to an optical switch, running that switch to a headphone amp, and the amp into the sennheiser rs base.
