Okay, on your 5740, the mode that I referred to as "pure" is the "direct stereo" mode. If at times you wanted to listen in stereo without the sub the most logical setting would be the direct stereo as described on p.30 of the manual. It bypasses everything(including the sub)except the master volume control. If, as you mentioned, the M60s were set large, bass output "both"(p.46)and you then manually turned off the switch at the back of the sub, the M60s would still get bass. In my view this would be an awkward way of doing it and my thought would be to use all "small", bass "SWFR" rather than "both", crossover 80Hz and then simply choose direct stereo if you'd want to listen to stereo full-range through the M60s alone. Also, disable the internal crossover on the STF-2.