Thanks for the input.
Since both the DAC-9 and the potential STA-9 or STA-6 are all that is between the sources and are maunfactured by the same house... and since I don't have the option of ´testing´, then it is PRECISELY why I am asking... not as a "generic" XLR vs RCA, but a very specific: on this case the RCA output of the DAC-9 to the RCA input of the STA-6 vs the Balanced XLR output on the DAC-9 to the XLR input of the STA-9 would there be any difference?
I understand from the replies that "no" is probably the answer, but I really think that most replies get watered down by comments such as 'investigate individually for each component'... that is EXACTLY what I am asking for, from the owner of the company that makes ALL the equipment!
But then I get answers like this one from Jason:
... it is not designed to be a lessor amp, we don't do that kind of stuff...
Oh, good then, if you don't do "that kind of stuff" then the STA-6 and the Ref20 are equally good since, because you don't do that kind of stuff, then every equipment is as equally good in your lineup? With all due respect, you DO that kind of stuff. It's called having different lines of equipment, where one is a bit different (or even better) but that difference or 'betterness' comes at some extra cost, so they are in different niches. And there is nothing wrong about that!!!
The STA-6 has certain characteristics, the STA-9 probably other, the ST-10 yet another and the REF20 for sure another. That is not bad! Otherwise, what is the point? Have a single line of the least expensive product and be done with it. That is obviously not the case!
So if STA-6 is just as good as the STA-9, why is there at all a STA-9 to begin with? If STA-6 is just as good only less expensive because of a very clever design, then phasing out the STA-9 in favor of the STA-6 would have been the route. Obviously there is something more that differs them other than "the SMPS was designed to be closely integrated with the amp module", I am asking for those differences. Maybe they are not so big as to merit mentioning them, but are they really both THE SAME AMP, 200 bucks cheaper because of the SMPMS distance?
I fully understand that being 'less good' or 'different' at something is not necessarily bad, hence the price points of different equipment. But to suggest that every piece of hardware on your AMP lines is 'the same' because 'you don't do that kind of stuff' is really not true! Sorry for the harshness, but it isn't. And, obviously, does not help users to make a decision. Or at least, will make users always only buy the least expensive product, which is not what we should aim for either.