Used full range, I much prefer SED 6550 in the RM-9 MkII over the El-34, primarily because of the increased bass drive and impact the 6550 affords. The ultimate choice is, of course, system dependent and influenced by listening preferences. For large scale orchestral works (Mahler, Rachmaninoff, etc.) and full-range speakers, the 6550 does it best for me.
