Dear Emailist: Two days ago I posted on Halcro's review and ( between other things ) give to him my advice to add the AT 666 to his Raven.
Like you say I'm ( till today ) convince that a vacuum hold down record is a must to have in any decent analog chain.
Yes, the improvement on the bass ( low bass/mid bass: tight, clean, pitch, no overhang, less coloration, etc, etc ) is really shocked and to believe we have to hear it, but the improvement is not only on the bass ( but only this fact is worth the effort to find the AT666 ) but at the other frequency extreme where we have more precise/definition on the high frequencies with a pristine presentation and ovbiously that in the midrange we find a quality improvement too. When the whole audio frequency spectrum " suffer " a quality improvement we have many other benefits in other reproduction areas: soundstage, focus, inner detail, less distortion, less coloration, etc, etc.
I know that many people are against these kind of Vacuum systems ( Walker, Halcro, Alvin/Monaco, etc, etc ) but I know too that many other audio/music lovers are in favor of it, if not ask to a Sota or Basis TT owners ( for name some ) that are very satisfied with the Vacuum hold down system.
I put in this way: ones you hear/heard it you can't live with out it!!!.
Of course that this is only an opinion and like every opinion a subjective one.
Trade offs??, of course there is nothing perfect ( yet ) out there: we have to be ( a must ) very carefully to clean perfectly the AT vacuum mat and the records side ( time consuming )that goes directly on the AT mat every time we play any record/LP, if not the dust ( small and invisible ones ) pass to form part of the recording ( stick ) and ( over the time ) your records could convert a little noisy.
If any one can live with it then the AT 666 add-on is worth the effort, you will enjoy it for ever.
Btw, Emailist IMHO you have to leave the underside of the AT666 like it is ( I already try something like you posted and does not works in good way ):
+++++ " The AT666 exhibits no kind of ringing when tapping it once it is placed on the platter. " +++++
this means its working right on target!.
recondition??, I own at least four of these AT666 ( old ones ) and what I do to " recondition " the rubber seals is only to clean/wash with water ( tap water ) and soft soap, then dry with a cotton clothe and finally I use a stick tape ( scotch ) over the out and inside rubber rings to take out any small dust, it works.
Emailist very good " move " with your AT666!, enjoy .
Regards and enjoy the music.
Raul.