Questions that didn’t fit into any other category so we had to create one for them.
Solid State Logic is a manufacturer of analogue and digital audio consoles for music, broadcast, post production and film, founded in 1969. It’s mentioned various times in throughout the KLF catalogue: The Manual has a short snippet about them, it appears in Disco 2000’s I Gotta CD and, most notably, the 1991 version of 3 a.m. Eternal which claims to be performed ‘live at the S.SL.’.
The reference in 3 a.m. Eternal points towards said range of mixing desks, most likely because it was recorded using one, so you could read it as ‘live at the mixing desk’ (which pretty much sums up all singles from the Stadium House trilogy).
(Image taken by Jon Gos from Kampala, Unites States [CC BY 2.0], via Wikimedia Commons)