Tube or SS doesn't matter. There are low power demand and high power demand devices in both camps and 500W is probably not enough for what you have. For a rough estimate a typical power amp is at most 50% efficient. To put out 200W (100W x 2) would require at least 400W from the line. The sub probably has a more efficient type of amp, but if you figure 100W for it, 25-50W for the CDP, and another 25-50W for the preamp you are over 500W.
600W might do it and 900W probably would. A better way is to take a look at your equipment on the back somewhere near the power plug. It should say how much power it needs. It may be listed as VA instead of watts but for your purposes it is the same thing. Add them all up and that's the minimum you need.
Since the 120VAC lines in your home come directly from the 240VAC lines, if your 120VAC lines are sagging (brownout) then the 240VAC lines are sagging right along with them. Hooking up a 240-120 isolation transformer won't help your situation at all.
Maich, using the same 50% calculation above, 6000W of amp output would require 12,000W of input power. That's 100 amps on the 120 side and 50 amps on the 240 side. That probably exceeds the ratings on the transformer and the lines. However, since you probably don't use all the power and it would only draw that much on maximum peaks you are getting away with it. It may be restricting your dynamics though.
