It could be of use.
You'd just have to figure out how to get +/-15VDC to it.
The +/- VDC output out of the 401 is Tip: +15V, Ring: -15V and sleeve is ground. But, I have no idea how this box is wired. Other than that, it's plug and play.
I bought my circuit module from EML in Jan.1979 and paid $45.00 for it.
$450.00 is too high a price. $150.00 might be more like it. Unless, they're hoping to get some bucks off the "vintage" market.
I make a similar module that does the same thing. But, it has a LED to indicate when the preamp level is reaching a 5V signal level, a LED to indicate when the gate is active and an inverted envelope output in addition to the typical envelope output.
My entire module is around $200.00 and the assembled/ tested module board is only around $80.00.
That's comparable to other modules of the same type in the current market. So, there are options available.
So as an EML 100 owner then this box would have no use for me without modification? It's not just plug and play?