Bryston Bit 15

I was considering trying a Bryston Bit 15 IS(just the isolation transformer) but I'm wondering if the voltage output would be too high given that the input is usually around 122-123v. If anyone is using one in their system and could compare the input voltage to the output voltage I would appreciate it.
At 122-123VAC your voltage is perfect, and it will be essentially the same at the Bryston's output.
Thanks, but if it raises the voltage by even 5 or 6 volts I wouldn't feel comfortable running my system with it. 
... if it raises the voltage by even 5 or 6 volts I wouldn't feel comfortable ...
I'm not sure why you fear this. As I stated, the voltage out is essentially the same as the voltage in.

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Because of this thread.
I don't think you can fault the Bryston as the second 'table also developed problems after the Bryston was sold (if I'm reading the post correctly).

I've had a BIT 15 in my system for over four years now and it's managed to protect my gear through multiple brownouts, blackouts, storms, etc.
The only part that concerns me was whether the output voltage of the BIT15 was increased vs. the input voltage.

For the most part, audio electronics should be able to operate within a +/-10% range.  A range from 115 to 125 volts is just fine because pretty much all audio electronics have some sort of voltage regulation when converting this to DC.  That being said, it could definitely affect the sound quality if it's widely outside of this range.  Anything much under 115V will have a very weak audio output (no impact/attack/muscle).  Anything over 125V could push too much of the "solid state/harsh/sterile" character.

I'm not sure what was happening in that example thread where the turntable was failing -- maybe the turntable doesn't have voltage regulation and is just running off a straight transformer from the A/C?  Turntables are different beasts and I don't have the experience to comment.  I do know that the speed operation on certain turntables are critically based on the 60Hz waveform coming in from the A/C (if it's an A/C motor instead of a D/C motor).

Isolation transformers could have winding errors.  You could definitely get a transformer what was increasing or decreasing the output voltage.  They are auto-wound and it's a random outcome.  They usually do not measure the voltage gain output during manufacturing because of cost issues.