step down transformer recommendation 100v to 120v

I own a pair of Exclusive monoblocks M5a that were design for 100v (japanese market). My preamp and cdplayer is made by Accuphase and they also run in 100v mode. I am wondering if there's a step down transformer you can recommend for this kind of equipment. I also hear that units made for 100v can easily be 'redialed' for 120v. if so, how can that be done? I am aware of a few websites in the U.S. that offer step down transformers but I am not familiar with their reputation. Can a transformer affect the sonic quality of this kind of equipment? is there such thing as as a hi-end transformer of this kind? any help is welcome. I have checked out a few threads on the web about stepdown transformers but they seem pretty ambiguous if any. when the question about "sound quality" degradation comes up it seems like the answer rather dodges the question. anyone out there with solid experience in this arena?
the current transformer I am using seems to work fine. however, at times, it seems to make this sort of "white noise" whenever i run the amp at high levels. perhaps i am asking too much power at once from the transformer. my amps are rated at 600w per channel drawing 400w each from the outlet. I forget the preamp specs but i think it is around 200w and the cdplayer is close to that too. any help on how to buy the right kind of transformer is welcome. thanks!
You have a strange set-up. Power amp that produces more power than it consumes from the mains; pre-amp that consumes 100 watts and cdplayer also!
I think that you need to take another look at your equipment specs and rethink this 'problem'.
BTW, your '100v' equipment should work on nominal '120v' outlets.
I might be wrong about the power output the monoblocks make. However, they read 400W - 100vAC 50/60hz on the back of each monoblock. The preamp reads 75W - 100vAC 50/60hz and the cdplayer reads 25W 100vAC 50/60.

could you also explain why should 100v equipment work on nominal 120v outlets? I thought that most manufacturers in Japan void their warranty if 120v is involved.
Accuphase can reset the voltage from 100v to 120v. They just re-solder a wire on a different tab on the main transformer. They do get some good money for a relatively simple conversion.

I would not run 100v equipment on a 120v! It may work & sound fine, but you're just asking for premature component failure.
Multi-tap transformers of that size are rare. I would suggest something like a Signal DU-2 or DU-3, if you're willing to put it in an enclosure. They are quieter than most, are Q rated, and shielded. Either is capable of more amps than wall outlet but I like to oversize by double.

The best power transformers have the narrowest bandwidth so "audiophile-grade", for these, is nonsense. They filter and regenerate the AC and are the only kind of power "conditioner" I would consider, personally.

The following link is not specific to your needs but has useful info.
is there another unit you can recommend other than the Signal?
You can try marine distributors but be careful about the specs. A single core 3.6 KVA might be half the currrent as a dual core 3.8 KVA.