I would not worry much about riders in this case. Neither board is going to meet a rider where the band coming in will even care. Basically, whatever rider that any of those three consoles meet, the others will as well. As far as the difference, I personally would rule the K2 right out. The K series Soundcrafts don't really sound that great (there are certainly better sounding Soundcraft models) and had some real maintenance issues. Buying one used could be risky since that specific model does have some known issues. Now, comparing the GB4 to the Allen Heath GL2800 is a little tricky. In my opinion they both would rate very closely in quality. If I had to pick, I think I like the GB4's preamps and EQ a little better, but not much. It's really more of a "feeling" than an obvious audible difference. If it were me choosing though, I would say that they are close enough in Sound Quality that I would base my purchase on a combination of price, availability, and layout (features). If I remember right the GL2800 is an eight bus board, and may even have 8 auxes.
The GB4 is a 4 bus board and probably has 6 aux sends. In a live environment, 6 seems like bare minimum to me. 8 would make me much more comfortable with my purchase, not to mention 8 buss as compared to 4 bus. If you do decide that 4 bus is OK, maybe you should give
the Midas Venice 320 a look. As a FOH engineer I would gladly sacrifice the features of the other boards mentioned and would opt to use the Venice each time. Even if I had to cut a few inouts from my rider to fit into the Venice (24 mono channels). The Venice is head and shoulders above the rest as far as Sound Quality goes. They are very durable, and offer an excellent warranty with an excellent Service Center (in Minnesota). What you need to be aware of before getting a Venice is that it is short on a few features, but those things are easily and cheaply mended and worked around.
First, it is 4 buss, and has 6 auxes. 2 aux sends are permanently postfade (labeled FX), 2 are permanantly prefade (labeled mon) and 2 are switchable globally (labeled Aux).
Second, the direct outs are post fade, post EQ with no option to change them unless you are willing to either pay the Service Techs $150 to do it, or are extremely handy with a soldering iron, tracking down traces on a PCB board, and soldering a new buss wire in place to make the bypass. This also would have to be done per channel and is tedious.
Third, the Venice series does not have a pad or a phase revers button. This is easily and cheaply worked around. You could just buy or make 4 phase reverse adaptors. 4 should be more than enough on just about any live stage. As far as the PAD goes, I have mixed maybe 150 or more shows on a Midas Venice. That would be close to 600 acts or more. In all that time I have NEVER needed a pad, or run out of headroom. The only time a signal has been too hot hitting the console is when certain instruments are run through a DI. The truth though is that if they red line the Venice, then they are probably also distorting some at the DI itself and the DI should be padded to begin with. In general I would consider this to be a non factor in my purchase of yet another Venice. If you are worried though, you could pick up 2 to 4 pad barrels.
Just my thoughts
