Interesting question!
I think a system, beyond the fact of being flexible or demanding, relatively and accordingly to his components specifically designed parts, must be optimally embedded at the end anyway...
And an acoustically very optimally controlled audio system is anyway always at the same time relatively flexible and relatively demanding...
A system which would be essentially mainly flexible or essentially mainly demanding, would not be an ideal choice anyway, but a functionnally specialized commodity for some needs...
Acoustic is the ultimate test for a system....And acoustic dont give a damn about flexibility or demanding performance of the system, acoustical ask for OPTIMAL synergy between system and room....And then transform a flexible system in a more demanding one or transform a demanding system in a more flexible one.... This is the power of acoustic controls....
Then a high end system must be OPTIMALLY working.....What i call "well embedded in the 3 working dimensions" which will make it more demanding and more flexible at the same time....