Fisher Tube Receivers rated vs. modern seperates

How do Fisher 800C and 500C tube receivers match up versus modern seperates? Ive had the preamp and amp sections seperated on my units (a $50 job from a competent tech). Ive tried subbing several other phono stages from recievers and preamps, as well as subbing just the preamp with some under $1000 preamps. I've also subbed some high power Denon monoblocks ($500) for the amp section.
Admittedly, none of my substitutions have been with Sterophile rated phono sections, preamps, tuners, amps, or headphone sections. However, I have made several switches with Stereophile Guide to Home Theater AA and A equipment. So far, nothing has been better than a well performing Fisher Tube amp. I know my preferance for 'that tube sound' has biased my opinions.
Well, now I have more money. Most people polled have said that to replace the Fisher with equivelent quality new stuff would cost $1500 to $4000. Most people say that the preamp section is the weakest. I'm thinking of trying a Rogue preamp in my circuit.
Anyway, what do you think? For me, the Fisher receivers have been an ultra cheap entry into the world of high end. Ive tweaked with isolation and vibration control, racks, cables, speaker placement, cleaning connections, power supplies, power filters and power cords, and interconnects and front end gear improvements. I've heard noticable improvement with each tweak, and now it's time to find something superior to my Beloved Fishers.
What would you do?
My vote for replacement value of sections (used equipment on AudiogoN):
Phono: $225
Preamp: $500
Amp: $800
Tuner: $600
Headphone amp: $200

Thanks for your time. I look forward to hearing what anyone with experiance upgrading from Fisher tube receivers has to say.