Interesting hearing about people using amps with different ranges of input impedance with good success.
I had forgotten that Oppo had mentioned using something like that if impedance was too high or low on amp.
You are correct. That tech(!) needs a lesson in Ohm's Law.
With an output impedance of 100-200ohms, any amp with an input impedance from 10Kohms and up will work fiine. Beyond that, there are too many options. Currently, I am using a Parasound Halo A31 which might do but I have no experience with your speakers and these might be too much for them. I have not used any tube amps in more than a decade.
I though you were using Classe!
Have used the Oppo straight to the amps and if so what did you think better, same or worst that with a pre-amp?
I acknowledged that it is available but I have yet to see one.
There's no law of nature in this universe(or others) that says the volume level of an amplifier depends on its input impedance!!! None whatsoever!
So you either misheard/misunderstood what he meant or he has no business being in the electronics business. As others have said, the volume of an amplifier is determined by two main things. Its input sensitivity and its gain. That's it and nothing else...
Now, on the question of valid input impedances, since the Oppo is a voltage source device with a low output impedance of 100-200 ohms, it will feed well into an amplifier with an input impedance is 100x or more, so 10K or greater. Most amplifiers fit this requirement quite easily as you may know.( BTW, basically the RCA output section of the 105 is an LM4562 with a 200 ohm output series resistor. The XLR has two 200 ohms in parallel for both legs to produce a 100 ohm equivalent resistance).
Now there are some amps which may have what I call 'exotic' input drive sections that are very reactive, i.e their input impedance varies widely with input frequency. For example, tt could be 10Kohm at 20Hz but 2Kohm at 20KHz. This can create problems to the source device as it constantly sees a fluctuating impedance instead of a constant one and hence change the combined frequency response (and possibly add distortion) of the whole setup... BUT I believe these amps are rare but in case they are not, then it would explain why some folks felt the direction connection of the Oppo outputs to their amps was a bad combination.
In summary, any modern amp should connect to the oppo just fine. If the input sensitivity of the amp is too low(e.g 100mV at the input to produce full scale output power), you can place HQ attenuators between the Oppo and the amplifier and will be right as rain...
Off,Off,Off ...did I say off? Why would you want to compress your HQ lossless audio? If its to keep baby quiet or neighbors happy, then turn the volume down or watch in your own sound-proofed HT room.
???... you meant to say an amp with HIGH input impedance is easier to drive, requiring less current from source....