Dunlavy SC VI's...

Yeah those are some very impressive speakers. Massive would be an understatement. I would also consider a used pair or a set of the 5s, the only thing is what do you do if you have a problem? I thought that the drivers where very carefully matched by Dunlavy and just putting an off the shelf set back in if you were to say blow a tweeter would not be the same thing.

one of the alltime great loudspeakers bar none.

Since the SCIVs do everything why would you consider mods? Look up Dunlavy SCIV on you tube.
I have a manual I can copy for you and I would be happy to share my knowledge of the SCIVs with you.

There is room for modifications. I would not imagine the drivers need any modification in that John used premium cones throughout that model. The crossover components are indeed suspect. Cheap resistors is where I would start. Capacitors will clear up some background haze and premium inductors would finish the project.

I wrote a review here about my IVa modifications for your reference.

The final places to look at is the interior wiring can be upgraded and improved. I have not done this yet, simply because of money, but no doubt will in the future. Some have sealer the interiors of their Dunlavy speakers and reported gains in sonic quality as well.

Other than these minor modifications, these remain state of the art. If you have any problems with your drivers, they are still available off the shelf. This was John's idea, was to be sure they were serviceable with off the shelf products.

As for matching of drivers, yes John was big on that, and if one was to replace tweeters one might consider this. I replaced my tweeters with a premium pair on my IVa's and did not match them, yet they measured nearly identical anyway. I think this was more marketing hype than an issue, but in your case the subject is mute in that I see no need to replace any of your drivers.

I just wish I could have such large speakers, as they are spectacular...

I owned a pair of scIII's and drove them with cary slam 100 monoblocks;the sound was fantastic.They did everything a audiophile would ever want so I can only think the VI's are even better.
As far as mods I did none;my only problem was a driver went bad and since they were out of business Bill Legall of Millersound resolved the driver issue;I highly recommend him for any issue you may have.He may even do mods on the crossovers if you want to go that route but I can't think of any reasons for modding these great speakers.