I don't know which model you have. If it is the newer ones such as the AVR-X3300W, X4300H, X4400H,... through AVR-X8500H, then yes, I would expect them to have the same pre out voltage performance as the X3300W that Gene measured. The higher models will likely do better in the THD+Noise spec but they should have no trouble driving the low gain (relatively speaking) RMB-1555 to well beyond its rated output.
Regarding speaker hiss, yes I do expect the hiss would be lower with the Rotel in a dead quiet scene, if only because it has lower gain, though I doubt you would hear hiss with even just the AVR when watching a movie and sitting a few feet away, unless you have very sensitive speakers such as certain Klipsch models.
By the way, if you look at the RMB-1555's input sensitivity specs, it says:
INPUT SENSITIVITY
1.5V
That's rounding, if you calculate it using the 26.5 dB gain, it will be closing to 1.47 V (i.e. a touch better).
If you can really get the Rotel brand new for just a few hundred dollars more, I would say it is a no brainer. Just make sure you either re-run auto setup (Audyssey) so that the unit will re-doing the leveling between channels if you are using more than 5 channels.
If you have been, and still be using only 5 channels, then there is no need to re-run Audyssey auto setup, but don't be alarmed if you find yourself turning the volume up a couple notches to reach the level you normally listen to.
An Amplifier amplifies the input signal with a "gain", in this case it is 2.65 dB, or 2.5 dB lower than the Denon's build in amplifier gain of about 29 dB, that's why its preamp has to work harder. That is, have the volume set a little higher, in order to send a higher voltage to the power amp, for a given output (Watts).
Again, that's usually not an issue for Denon AVRs to drive power amps with gain 26-29 dB and rated output up to 200 WPC. For power amps rated higher much higher than 300 WPC, one would have to be more careful in their selection of AVRs/AVC/Ps, and AVC/Ps should do better in general. You can take a look of the measurements of the Yamaha CX-A5000 AVC just for example, and note what Gene said about the pre out performance:
"CX-A5000 11.2 AV Processor
The CX-A5000 preamp output is certainly more robust than the typical Yamaha AV receiver many of which clip below 2Vrms output. This was not the case with the CX-A5000 as it was able to deliver a clean and unclipped 4Vrms output via unbalanced and about 8Vrms via the balanced output connections."
Review: The Yamaha AVENTAGE CX-A5000 Processor and MX-A5000 11-channel amplifier are for you if you have ever wanted reasonably-priced separates but didn't want to sacrifice features or performance.
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