I can't comment on the 5881 loaded model, but I had a JCM 900 2100 w/EL34's. I believe it was advertised as an SLX series and was supposed to have a butt load of gain. It was a decent amp, but definately needed a boost to get that over the top gain and to really get the goods IMO. I got a fairly good tone out of it and I got complements on my it, but honestly I think there are much better choices out there that would eat that amp for lunch as I didn't find anything special about it. If you're talking about the JCM 900 4100 stay clear . I've played at least a half dozen and they were some of the thinnest sounding amps I've ever played.