Sansamp Prgrammable BDDI Output

Hi,
i recently ran into the following problem:
On my Sansamp, the three settings i use are a 'normal' tone, one that emulates a hard driven tube amp with quite some overdrive and one with less highs and big boomy lows.
Setting one and three are fine. The boomy sound is set a little bit louder to compensate the lack of highs. Setting two is a little different. There is not as much dynamic range because the
more you dig in, the more you send it into saturation with a bit more compression and no audible increase in volume. These three, after some fiddling around, are well balanced in the mix.
When I play live, i mostly bring my Aguilar Tonehammer500 and GS212 cab and go from the 1/4" output of the Sansamp into the FX return of the Tonehammer.
FOH gets the DI signal from the Tonehammers DI out. This works well.
When i do not bring an amp and use the DI out of the Sansamp, preset 1 and 3 are fine, but when i hit the preset with the overdrive all hell breaks loose. That preset is MUCH louder on the XLR out, but quite allright on the 1/4" out.
Could someone explain why?