I've been thinking about doing one, what always gets me are the costs. I was calculating out stuff for a 48 channel (does that qualify as large?) line mixer (monitoring and mixdown) with fairly nice (but not inductor-based) EQ, 8 aux sends, balanced mix bus, 8-bus plus stereo, no automation, LED metering, TT patchbay. Parts price tag? Somewhere around $15,000 or $20,000... Time to build? Probably about a year or a year and a half of weekends to build, and quite a while to lay out the boards too. Faders alone are about $4000 (for the nice ones) or so. Printed circuit boards? Around $3000. Using reasonable op-amps? LM833? NE5532? Those are expensive enough when you need 500 or 1000 of them. Just the time aspect of the project seems daunting. More time than it took to build my vacuum thermal evaporator chamber.