Will rebuilt Quad ESL 57s take the place on a great $30K dynamic speaker?

My best result with Quad 57's was as follows -

Remove steel grils

Put them on stands about 18"  off the floor

Tilt the panels up to more vertical and angle in slightly

Amps - tried a few best by miles was Quicksiver 8417's - could go loud without arcing, plenty of punch, dynamic and massive soundstage.

For reference I had also traded pair of stacked Quads - awful in my view.

An audio buddy had the 57's set up with Decca Ribbon tweeter & Sequerra subwoofers - great system - biggest difference was the ribbon tweeter.

Don't need subwoofers when driven by the Quicksilvers.

Hope this helps.

My best result with Quad 57’s was as follows -
Remove steel grils
Put them on stands about 18" off the floor
Tilt the panels up to more vertical and angle in slightly

I have them on 20" stands, grilles off, vertical and toed in. Monoblocs under each speaker with 2’ of UP-OCC copper in Teflon. I find the toe-in to ear position critical. The "head-in-a-vice" gives the best imaging and detail.

The Quad 57s are astonishingly good in their areas of strength, exactly as the OP describes. They are definitely improved by being placed on stands and, properly serviced, they sound much better than a lot of people's experience of tired pairs with panel damage, failing EHT units etc. In particular, a good pair on stands have much better bass response, albeit limited in slam and extension. They are fussy when it comes to amplification and they don't like high powered amplifiers. They have limited loudness and playing outside of their performance envelope will only arc them and exacerbate any rattles, panel resonances etc. A lot of the owners I know go through periods of "can't live with them", can't live without them" angst but nearly always come back to the '57. Personally, I'm in the school of would love to live with them but unfortunately for the wide spectrum of music I listen to, I find them too limiting. But, I really appreciate them for their intrinsic qualities and as a landmark in audio design - and not beaten by the 63 of the subsequent IAG era iterations.

Unlike some here, my direct experience with ESL 57s is limited…I heard them at Victor’s in Chicago in 1972. He played a Decca cart and Int’l TA into ARC electronics. A Mozart chamber ensemble on Phillips…probably Raymond Leppard…it was divine. Next he played a Tympani by Magnepan. Bigger sound but that ethereal detail was absent.  Today, big Maggies have ribbon tweeters which bring the detail. For large scale scope, dynamic slam, no box coloration, with musically correct detail, aren’t 20.7s a legitimate comparison?  Anyone lived with both?

I have ESL 57s since 1975 and ESL 63s since 2000.  The 63s are in my audio system with two JL E112 subs.  The 57s are in my video system with two 15" woofers, not currently connected as I need to build a crossover.  

One must be careful with the amp for the 57s, maximum voltage is 33V.

To integrate the JL subs I use a single order passive high pass filter for the 63's amp and for low pass to the subs I use the crossover in the JL.