A few years ago I replaced my Adcom GFA 555 II with an Odyssey Stratos Dual Mono. I felt there was an appreciable improvement -- while I'm not always sure of the words to use for such camparisons, the Stratos seemed deeper and darker. (Of course, the Stratos was around 1300 USD used, quite a bit more than a used Adcom or even two.) Furthermore, Klaus at Odyssey is well known around here for being a straight up guy who supports his used equipment, so I suspect you'd not regret your purchase -- I certainly have been very pleased. So, although I'm not familiar with the mods in question, I'd 3rd the suggestion to go with a Stratos.
Worth noting, though, that you're contemplating spending in the neighborhood of 1000 USD, whether you do the mods or the Stratos. As Bob_reynolds says, it is possible that you might notice more improvement if you put the grand elsewhere, especially since you like the Adcoms (I liked mine too). Of course, a used Stratos is likely to resell well, so you could "audition" a used one for relatively low risk, and see what kind of result you get. (Though notice that the Stratos is a beefy piece, and the shipping expense may be non-trivial.)
My 2c. John
Worth noting, though, that you're contemplating spending in the neighborhood of 1000 USD, whether you do the mods or the Stratos. As Bob_reynolds says, it is possible that you might notice more improvement if you put the grand elsewhere, especially since you like the Adcoms (I liked mine too). Of course, a used Stratos is likely to resell well, so you could "audition" a used one for relatively low risk, and see what kind of result you get. (Though notice that the Stratos is a beefy piece, and the shipping expense may be non-trivial.)
My 2c. John