To my knowledge the E-line upgrade only applied the SA series of amps.
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The E upgrade involved replacing the gain cards in the amp, and mine is an S300. As I recall it ran about $500.00 and was well worth the $. Jon Soderberg is offering an additional upgrade on Threshold amps where he replaces the caps, and lowers the wattage, increasing current. A great guy, email him for more info. Tom
I forgot to mention that the original Threshold E upgrade adds balanced inputs on amps, and outputs on preamps. You can tell if the upgrade has been done by a small plaque they put on top of the unit which says the unit has been brought up to E spec. On preamps it involves replacing the entire main board, and will have the E power supply if they popped the extra $500. for it. Again, well worth the extra $. trich727