The Hartley woofer was actually a 24" driver. Matching subs with the ESL was for years unsatisfactory to most QUAD owners, but that was before the GR Reaearch/Rythmik OB/Dipole was introduced.
I made my own stands for stacking pairs of QUADS: three layers of 3/4" MDF glued together! Like @noromance, I prefer singles, also naked. Great on small ensemble music (Baroque, acoustic Blues, Bluegrass, Folk, Singer-Songwriter, etc.) and of course vocals, but with very-limited maximum SPL capability (subs help increase that). I have a pair of the QUAD front grilles made by Jerry Crosby, but no grill is even better. Ugly as hell, but oh well.