That is music dependent. A simple flute would be more sensitive to detect than an orchestra. But, I would not worry about .1%, or even more at times. There are some references around on this.
Also, is distortion additive, multiplitive?
amp - .05
receiv-.05
total - .1? .25? .0025?
Does distortion vs spl increase exponentially?
Well, that stand alone amp would be connected to a pre amp out, so we would need to know that distortion. But, for this, let's assume it is .05. You would add to that .05, .05% of that .05= .0525%, or so.
Now, pertaining to subwoofers...
Is distortion just as noticeble?
No, it is not as the hearing is much less sensitive in the low region for detection. Subs are rated in reviews up to 10% distortion.
Someone once told me that subs pretty much are made to output distortion, so you can use a amp with high distortion and wont notice a difference...
Thoughts?
Reorx
No, subs are not designed to have high distortion. Other factors are at play. Velodyne subs use servo controls to keep distortion very low