XXHighEnd

I am probably going to buy this:
http://industrialcomponent.com/opticis/opm210010.html
It is an optical usb cable.  I will also need a short usb A to B cable on the downstream side (going into dac), and will probably get this:
http://industrialcomponent.com/newnex/uh2abr0106.html
It is powered on the downstream side with a wall wart (no copper in it so it doesn't use the 5 v usb)... optionally I can buy this battery power supply:
http://www.amazon.com/Socket-Communications-AC4009-541-Li-Ion-Mobile/dp/B000309YMM
There are probably cheaper battery supplies I need to look into... how about this one:
http://www.bixnet.com/5v7libapa.html

Anyway... what do you think?  This would move the computer/HardDrives closer to me to control and Isolate the dac/stereo from whatever computer interference.

Theories are good I think. There may be (or will be ?) jitter implications though. It's really something to test out ...

It's going to be a bit of an expensive test I'm afraid.  Some over at Audio Asylum say it has worked well for them.  But ya I'm afraid of adding jitter, so if it doesn't sound as good as my 1 m of regular cable, I'll go back.

This opticis cable plus battery pack did not work out for me.  Sounded worse than my, now, 6 feet of wire usb cable.  Someone at AA hinted it might be my dac not liking the battery pack and other usb dacs may not have a problem... oh wellz.  I tend to think the optical/conversion stuff going on is causing jitter/problems? dunno... didn't sound as good.

Because the Opticis didn't work, I'm trying something else.  Next to my music room is a hall space with a closet.  I'm putting the HDDs in this closet and drilling a hole through the wall to pass the firewire through to my laptop.  I'm using 6 feet of Firewire cable now and want to go up to a minimum of 3 meters to make this work.  4 meters might work better... but I can make 3 meters work.  ? is, does the length of my firewire cable coming off the HDDs to the computer make a SQ difference?  I wouldn't think so, as long as I don't go too far? 
I know this for sure, that SQ varies with the USB link from my computer to the usb-dac; so I'm keeping USB cable and length the same as now.  But the file from the HDDs loads completely in memory (right?) before playing so, unless the Firewire cable from the HDDs is so long the signal drops data?? which I wouldn't think 4 meters or under would? I shouldn't suffer SQ lose.  Do you know?

You are right about everything;
As long as the longer cable gives you a connection, there's no problem. And *if* there is a problem, you'd just get errors. This is a normal "data" connection you are talking about, different from SPDIF ...

Btw (unrelated to your subject), for my XP machine I use a run of 10 meters Firewire towards the reclocking (Fireface) soundcard. It seems to "grey" the sound a tad, but not more than Firewire interfaces differ amongst eachother. IOW a good Firewire interface card is more important than the length of a cable (the worser interface being less able to control the longer run of cable).

One other thing :
Putting the HDDs in the toilet might be a nice gadget. But before you do, maybe you could open the cabinet they're in (I don't know anymore what you have), shut down the fan in there, leave the cabinet open and keep track of the temperature of the disks. Nowadays disks just can have it and you must be with your ears on them to hear them. Mine (4) are right in the open stacked onto eachother without (air) space in between them ...