Thanks for all the help. So I am looking at a set of MR94A's with 291 series drivers..I understand you can replace the Symbiotic diaphram with an aluminum type found in the 288, essentially for all intents and purposes this makes the 291 into a 288...The other issue would be what the best match in OHM rating on the diapram would be with flea powered single ended pentode 6BQ5 tubes?