Any one heard these and compare the top reference level amps under 20K? Example Spectral DMA360 vs. Pass Vs. Mark Levinson Vs. Audio Research Ref210 Vs. Air Tight ATM3? Is it all about taste and speaker match or does anyone stand out significantly over the other? Should one MUST select a speaker first? or can a speaker be added to a reference level amp later? i.e. would one be limited to the speaker match with any of the above amplifiers?