|Have you folks tried using the RPX-33 with an IEM? I have a set of UE-10 pros and am interested in a high-end amp.
I'm not a technical person, so my ability to properly explain is somewhat limited. But my understanding is that Rudi's high-end amps (such as the RPX-33 and the RP010, and the RPX-100) all use *no feedback* in their design, and are pure delicious, unadulterated Class-A. This a purist approach
which is one of the chief reasons they sound so friggin' great; transparent, clear, full, and precise. That pure Class-A goodness gives them that tubey yummy-ness. But going that route isn't always without some consequences for some people.
IEMs are hyper-sensitive by design, this is the reason (for example) Ray Samuels designed a separate amp specifically for them. Using feedback can lower the noise floor to a level that won't have consequences for an IEM, but is not necessarily the purist approach. So there are some design trade-offs to make an amp 100% compatible with all IEMs.
I can't report on any IEMs with the RPX-33 or the RP010, as I don't have any. I can say that with "normal" headphones, noise floor is not an issue. My RP010 (like all Rudi's high-end designs) has two jacks, one high-gain, and one low-gain. I have already reported that out of the High gain jack, with my very sensitive Sony R10s, there is a *teeny tiny* level of hiss audible from the amp, but it's at such a low level, analog tape hiss from most CDs is at a much higher level and this sound gets lost anyway once actual music is playing. (This low-level noise was not audible out of the High jack of the RPX-33; but that's just a sign of how much more transparent the RP010 is). I doubt highly this noise would be audible out of any other headphone than the R10, certainly not any Sennheiser. If that bothers you, you always have the Low-gain jack out of which there is absolutely ZERO noise.
Bottom line is that the RPX-33 and the RP010 (and I presume the RPX-100) are designed for "normal" headphones. They are designed to give you the RAW, PURE signal-- you are staring directly into the very heart of the amp, not being held back at a polite distance.
So, I can't say Rudi's better designs are "incompatible" with IEMs, we already have one report that says otherwise.
My Dad has a pair of better quality IEMs; I'll ask to borrow them and will report back.