Does Using 1/4" vs. XLR, bypass pre amps?

[Reggaesoldier]

So I was using my DMP3 into a Behringer mx802a mixer via (bal)1/4"-to-XLR cables. And (unbal)1/4"-to-1/4" into a fostex MR8's 1/4" (unbal) ins. I was told that I should use the 1/4" jacks in the mixer or even better the mr8 to bypass the pre amps. Is this true? Do I have to use the 1/4" jacks on units I want plug my DMP3 into to bypass the internal preamps on the other unit? Does this make sense? Its really confusing me. I also was wondering, if this is correct, what exactly does it do to the sound when I go from the DMP3's (bal)1/4" outs to the mr8's (unbal) 1/4" ins? It almost doesn't seem right to me. Again if this makes no sense let me know?

Also, if this again is true, why is it that only the XLR ins are preamped and not the 1/4" either? Thanx in advance to anyone who can set me straight.