Murphy,
I've also read quite a few posts stating that users who have heard both prefer the ARC REF 75 over the 150.
GG
My apologies to the OP if I stray a little from the main element of this thread however I do feel that a little clarity and balance may be in order here .
I suspect that you are referring in part to this thread over on AA ? ~
http://www.audioaficionado.org/audio-research/24023-my-first-audio-research.html
Having myself demo'ed both the Ref 75 and Ref 150 with ML speakers as well as Wilson , Quad ESL , Harbeth for the sake of expediency I shall re-post my initial thoughts from the aforementioned thread ~
" I do feel that we need to consider this point most carefully when comparing the Ref75 vs the Ref150 .
Starting with the most obvious consideration ~
Of the few opinions that we have had reported to us , here and elsewhere , how many were formed as a result of an A/B demonstration incorporating the same ancillary equipment and/or system .
What were the relative running hours clocked up on each unit . The same model will perform differently with 300 hours on the clock as compared with 1000 hours , let alone unmatched hours upon two disparate models .
Were the valves fitted within each amplifier stock ARC factory Sovtek 6h30's and 6550's or a combination of alternates .
Were the KT120's utilized a matched set for both amplifiers , disparate output topology's making this an exponential factor even more important maintaining the Ref 150 at factory output distortion levels .
microstrip also touched upon another , perhaps subjective point, in ~
" IMHO the REF75 asks for an "easier" and less ambitious speaker "
Perhaps 'less demanding' would be appropriate here , however his point remains germane as to the voicing of speakers , particularly the mid-range .
Where less dynamics and scale are required of the speaker I feel that the Ref 150 excels in the mid-range equitably as well as the 75 , however , the converse can place the 75 noticeably out of its comfort zone . "