Yeah, being weird is what makes it cool, if they screw with that there's no reason to buy one.
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So I finally got an E/90 energizer (it's really an amp) for my ESP/950, I saw one on ebay for cheap so thought "why not?" Anyhow, after much listening between it, a Woo WEE (hooked to an Accuphase E-560), an SRD-7 (with same amp), and my SRM-717, I can say with certainty that... I can't tell much difference at all. Seriously, whatever differences that exist could very well be attributed to me thinking the SRM-717
should sound better (confirmation bias). It could have slightly better bass control and be a touch more refined on the top end, but it isn't much to take note of. In fact, in blind testing I can't really determine which is which with any regularity (~60%). However, I can tell the difference between any of those and my EC Electra, every time (it's considerably more "interesting" and euphonic).
Determination: If you have an E/90 just keep it, SS upgrades are rather pointless, IMO, despite its light weight and rather cheapo feel. However, if you want to go with tubes, there's a good argument for it (and something like the Electra or BHSE is a great addition if you are planning on buying any Stax `phones too). The only thing I really recommend is buying a more robust power supply, which are available for <$40
through Digikey. It offers more current, doesn't get nearly as hot as the OEM, and is much more plug-in friendly than a fat wallwart.