I've just started studying the JCM 900 series. Don' know much about the 900 series except that I see a lot of bad things about them. What is the difference between the 4100 and 2100? I see that the 2100 is called an SL-X. Looks like the 4100 was re-issued so it must be more popular? I just came across a broken 2100 real cheap and wonder if it's worth $200-$300 as-is.