Wait a second here. Either I have noticed some problems with what is going on or I just don't know what I'm talking about.
First of all, 8 Sundowns is not 20,000 watts. They are stable to .5, but they aren't 20.1s, and really shouldn't be run any lower than that except for burps. Even at .25 or .35 or whatever they won't be putting out more than 2,000 watts though, if they even do that. Unless you are on a 16 volt system or something which I know nothing about. 8x2000 is 16,000 watts, so at the very most you are putting 4000 watts to each sub. Anyway, there is no reason to run the Sundown that low, especially strapped. The gains in wattage when you go below 2ohm strapped are negligible and not worth ****ing up your equipment for, unless of course you have unlimited funds which you do appear to have //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif
Second, and I don't know very much about this, but isn't the resistance only a function of the amp and wiring? In other words, the resistance the amp is seeing from the voice coils makes absolutely no difference on the sub end, right? I thought there was no difference to the subwoofer between 1000@1ohm or 1000@100ohms. If so, it shouldn't make a **** bit of difference what ohms your amp sees because the sub doesn't discriminate.
Edit: I see the Sundowns actually do more than that strapped. At .5 strapped they do 4400, which would give you close to 18000 total watts, but that is only meant for very short burps. I can't imagine what kind of damage you are doing to the amps and subs with clipping and distortion and voltage drops and all that from running them so low while strapped. I highly doubt you are seeing 4400 watts out of them for very long either, once they heat up, in fact I'm kind of surprised you haven't set anything on fire with them yet.