After researching DCX/DEQ IO mods, I pulled the trigger on replacement output cards from Simon Ashton for my DCX.... to test the waters.
Any sonic/audible improvement?
Holy Sh*t yes. Extremely Hi-Fi. Silky smooth and a deeeeep soundstage.
Hard to install?
Not too bad, but the wiring does require some planning (especially if using the input cards too) and the use of a needle point soldering tip. Don't bother trying with a chisel tip no matter how small, nor a butane pen like I tried at first.
Worth it overall?
That depends on how much time and equipment is spent on the project...alongside the reliability of your our own handy work. The cards aren't inexpensive, but you simply can't buy a premium DBX or Ashley that sounds better than this either. Took longer to install than I had intended but, soundwise though, it's the best analog preamp I've experienced to date.
The modded DCX driving a DC-300A Series II approaches the sound quality of the NAD C390DD. That's a big deal.