a DSP speaker fed by a source saturating it with jitter, RFI etc. is not going to sound very good and will not do justice to the speaker
I would agree with this. When my 508 failed, I switched temporarily to our DVD player as the source to the processor for playing music. That sounded awful... I then connected the Logitech Squeezebox and all was good with the world. I would also agree that, if you are buying a HiFi with no intention of upgrading any time soon, a balanced system is what you should be aiming for.
I guess I should refine my question: If you're planning to build and upgrade a HiFi in stages, which priority do you place on which components first? To my mind, getting the sound signature right is the priority (I would argue, in a good system, the speakers tend to be the greatest variable in what sounds right to
you) [In the case of the DSP speakers, some of these decisions are made for you (to great effect)].