09-25-08: CwlondonIt's not that complicated. The SLA1 and SLA2 accept single-ended 1/4" phone plugs, balanced XLR, and balanced Euroblock. The SLA4 accepts single-ended 1/4" phone plugs and balanced Euroblocks.
Re ART amps, are the "Euroblock" connectors recommended?
If I have to spend big bucks on weird cables, this amp might no longer be as "cheap as dirt"?
In either case, if you have single-ended RCA interconnects, just get some RCA-to-1/4" adapters. If you used balanced XLR, you can plug them in as-is to the SLA1 and SLA2. If you want to use balanced XLR to the SLA4, you would replace the XLR plugs at that end with Euroblocks, which cost about $1 apiece from electric/electronic parts suppliers.