bypass pre's on digi mixer?

[thedude400]

I know when I used an art mpa pre with my old aardvark, the pre's almost seemed to cancell eachother out. There was a very vague signal coming thru when I plugged it into the aardvark's 1-4 (phantom powered channels but with phantom power turned off). But when I plugged into the last 4 channels it worked fine.

If I patch in a joe meek pre in one of the xlr in's on my new digi mixer, will it just automatically bypass the tascam pre or will it use both?