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.