the Smyth SVS Realizer is a practical demonstration that typical electronics don't seem to have a big problem with presenting a convincing synthesized soundstage of a specific set of loudspeakers in a real room
they sidestep a lot of the modeling with real measurements, mics in your ears in the real room, in front of real speakers from mono up to 7.1 multichannel setups and calibrate as you turn your head through specified range of angles for your personalized hrtf
then they do the same for your circumaural headphones - they supply a Stax Lambda system as a default for those without their own preferred audiophile cans and amp
the result is very good - you can localize the virtual speakers as well as the real, compare in seconds by just lifting the cans off your head, tilting them down so the head tracker can't see the target
the reductionist position is that good electronics, a complete ADC/DSP/DAC chain inserted gives "out of the head" stable, "realistic" soundstage of "those speakers over there, in this room" - because the phase, frequency response conditions needed for the amps ADC and DAC are trivial
http://smyth-research.com/technology.html
after hearing a full personal calibration demo of the full Smyth system in a 5.1 setup it is ROTFLAMO funny reading most Head-fi "soundstage" discussions of even headphones, much less claims that specific amps have a serious role in "correcting" soundstage, "in synergy" with certain cans
at least crossfeed circuits or plugins, Dolby Headphone make real differences - but still are pale shadows of what the Smyth Realizer does with personal calibrations and active headtracking