The Fairchild part seems to be a good sub but I've never used it.
I wouldn't be concerned about the squeal at this point. You're starving it for voltage/current so it may not behave perfectly.
You have 4 50+ amp FETs in parallel in the power supply. It's unlikely that you'll damage them with 5 amps of current unless they overheat (which they won't do if they're clamped).
If nothing (twisting the various components) makes a difference in the idle current, remove the limiter and insert a 10 amp fuse in the B+ line to see if it will power up. If it blows the fuse, pull the rectifiers to see if it will power up without blowing the fuse.
Does it look like either of the output inductors has overheated?
I tried powering up the amp with the higher current limits, but the idle current never stabilizes. Sometimes is wanders between 3-4 amps, while at other times it pegs the current limit (at both 5A and 9A). This was without twisting the components.
I then tried twisting the inductors and the transformer as suggested when the current was varying between 3-4 amps. I could not find any component that significantly caused this current to rise or fall significantly. Even when the amp was "stable" pulling 3-4 amps the power supply was still squealing also. I checked again for DC on the speaker outputs, but there was none. I was only able to look at the amp for about 20 minutes today, so I will have to wait until the weekend to pull the rectifiers and then try again. My spare parts for the blown transistor should be here tomorrow or Friday also. Should I still keep out the new Q121 transistor or install it before trying again? I have some spares if Q121 blows again.