I've read the Adcom GFP-555 preamp has been modified/upgraded in the past,supposedly with great success. I'd appreciate remarks from anyone who can personally attest to the GFP-555 being worth modifying (or not!!)and/or can recommend folks who currently do modify/upgrade the unit. I know there was a gentleman in St. Charles, Mo. who used to advertise in Stereophile who did so, but I've forgotten who he is and he no longer advertises.
A GFP 565 recently listed here in condition 8/10 for less than $300.00. That's probably less than most modders want to modify your GFP 555. In all honesty, why bother modding your 555? Also, after the mod(s), the only tech who'll feel comfortable working on your 555 is the original modder..
I'm well aware that money would be better spent on a different preamp altogether. I have a GFP-555 I've had for years sitting around gathering dust, and I simply was asking for input on the pluses & minuses of modding the GFP-555 itself.