Hi, Elizabeth's points are right on. If cheap enough I would lean towards the originals and budget for a rebuild at some point.
I have a 989's and they are amazing, but each has required service. The services were painless, except maybe the shipping. The 989's are large and the original shipping boxes aren't all that great.
The main issue, IMHO, is once you hear ESL's it's difficult to listen to more conventional designs. Another bonus, if you can call it that, is that the Quad's do it with low watt (tube) amps.. I'm using a 25 watt EL 34 amp with, to my ear, great results (with Pangea power cords-thank you Elizabeth for your review of those cords). The original Quad amps, I believe, are 15 watts and more than enough to drive the 57's. So, be carefully with the 40 watt amps - you might consider selling those and getting the standard 15's.
Best of luck-enjoy
Note: consider ofc speaker cable that is either plated with silver or has silver strands mixed in--- that type of cable did make a difference on my Quads.