I have heard several of his mods. And the are better. More detail, quieter, stiffer power supply. You may want to consider buying one of his newer models. You can trade it in or sell it. I owned a 600 with all wonder caps and I loved it. I liked it better than the GK Mod. Mine was stock with all Wondercaps. We compared 3 600 mods and the wondercap mod unit was superb compared to the other two. I don't have any idea why but it was excellent. If you have planars or electrostatics this amp is hard to beat. I agree with Rrog and Ejlif. Many of us have items modified then sell it shortly thereafter and if you are not careful the mods vs resale oo not translate into added value. Many times you lose funds on the mods. A already modded Kay 600 sells for under $1,000 on these pages most of the time. Some more some less. It depends on the times I guess.
moscode 600 " the newest mods"
I have a maxi version 600. I bought it new in the 80's. It's been a very good amp and I still appreciate it's contribution to my system. I notice that George Kaye the original (engineer) designer of the Moscode is now offering some major mods and a rather different approach for his original design. The description and resulting changes to the sound are very alluring. The upgrade package could run into the $1500.00 range. I obviously like George Kaye's ideas on reproduced sound and I'm constantly trying to improve my set up but, it's a lot of bread, so I was hoping some of you may have had some of these modifications carried out and might be able to offer some comment on the results. I would actually appreciate any insight in helping me arrive at a decision.