Tvad, admittedly I don't get out much. The only top players I've listened to closely are Zanden, DCS stack, and top Reimyo(RBCD comparisons only), as well as comparisons to vinyl in my own system and to stock 777ES and Theta Gen 5a that I keep for reference. IMHO, none of the above approach RBCD on my battery-powered SCD-1, which is based largely on Reference Audio Mods ideas & parts, twists from Allen Wright and Yamada-san, and also various experiments of my own. I've put some things into it that from a T&M and risk perspective are not particularly viable from a commercial modder's perspective, but having moved progressively through many iterations of upgrades, my sense is that you can get fairly close to this level of performance for $2-4K spent with RAM. Unfortunately I have not heard the VSEI L7 mod, which in balanced version prices out for around $3K and offers the benefit of a productized, drop-in, warrantied purchase.
One thing I know is it's all about improvements to clock, power, and analog section. The "heart" of the unit-- the digital section and DAC-- is very strong. Too much emphasis is placed on the latest developments in the digital domain(e.g. upsampling, parallel DACs, etc.), while ignoring built-to-cost compromises in other critical areas. If one accepts this viewpoint, then these two Sonys remain good platforms for continuing mods.
As you imply, mods are not for everyone, as most of the value is lost on the resale side. But if you are a keeper, the Sony has almost unlimited potential.
