It doesn't seem like there is anything there that cannot be solved. I would still like to hear about the fuses.
Before blowing more fuses or buying bigger step-up transformers, you may want to gin up a way to use the old light-bulb trick which has been used on countless amps: In your case, you would need to rig a safe way to put a 100 Watt light bulb in series with the 120V input to your step-up transformer. Rig this with whatever parts you need to make certain that you have NO 120V exposed!
Once you have this safely set up, simply power up an amp. You should notice the light bulb flare up for an instant as current rushes in, then rapidly fade to a very low glow. If the light bulb gets bright and stays bright, you will have an indication that the amp is drawing excessive current and needs further attention.
The advantages of this approach are that it involves only a couple of parts from the hardware/home store, and that, if the amp is indeed drawing too much current, the light bulb simply drops more Voltage, thus protecting the amp and even the fuse in most cases.
Post back if I have been unclear about any of this. Better to ask questions, etc.
