KT-88 vs. EL34

First of all, thank you for your replies. I will address all of your questions to date. 
1. Amp is wired as a pentode (or tetrode, depending on how you view beam power tubes) and not triode. Often thought of triode wiring and even single ended using one of the tubes but the power hit would be too great, maybe.
2. Not using AR4x. Those were my wife's college grad presents and have been out of sight for over 50 years (we just celebrated our 50th anniversary). Hooked them up for fun and they worked!
3. I am currently using Canton Karat M70s, woofers facing out. Not too efficient and 6 ohm average. Current amp is SS, a B&K AVR-307 (150w x 7) in two channel analog mode, used for stereo only. I like switching in the tube amp however; its intrinsic linearity is a pleasure to listen to. No edginess (but a little bright). Based on everyone's good advice I would really like to try the conversion to EL34/KT77s. a few resistors and Jond's 4 Gold Lion tubes and I'll be set to go.

I will try to track down the old A-C forums to learn more; Thanks for the suggestion bdp24. Andy8400.

KT-88 or EL34 doesn't matter 1%.  It's all about the overall amp design.  No point in conversions if the basic amp is not a good design to start with. 

bpoletti, you may be right. I had heard however that some, including possibly the above responders, have converted and found the EL34 to sound "better" on the same amplifier so the design wasn't a variable. On the other hand, the outlay of this type of tube amp generally is relatively straightforward. The one important variable that can truly influence the character of a tube amp IMHO is its output transformers because, as an inductor, evenness, peakiness, etc. are most influenced here. It's possible that the different loading that the EL34s place on the primary could account for the differences in sound. What do you think?

6L6GTB sweeter than EL34 - RCA black plates. 

Modjeski designed his RM-9 specifically for use with the EL34 (four per channel for 100w/per in the Mk.1, 125/per in the Mk.2), his RM-200 for the KT88 (two per channel for 100w/per at 8 ohms, more at 4!). But the 200 can also be run with KT-120’s (though not the KT-150---the transformers get too hot at the required plate voltages).