Yanitzch...
Yes the audio output from TOP 1 (Fender Amp) is definitely lower than the others HOWEVER, I noticed that increasing the GAIN for TOP 1 does not significantly increase preamp distortion like it does with other amp models .... so, try having the GAIN up well past 1 o'clock and see if you get a better volume structure. It worked for me. I do like the Fender Amp models (primarily the Twin) and I run them with a significantly higher Gain setting than with other models to compensate for the relative gain differential. The sound is still very clean. What you can also try as an experiment for TOP 1, is to put the Gain all the way up full, lower the Channel Volume so you are not blasting yourself, play some strong chords (with guitar up full) and see if the sound is still clean enough for you, if not, back the Gain down a bit (raising the Channel Vol to compensate) until you find the sweet spot where the Gain setting is still providing the clean tone of a Fender Amp. When you're there, you will probably find the Gain to be past 1 0'clock somewhere which in some of the other amp models will definitely be adding grunge, but not with the Fender amp (or so I've found anyways). Then crank the channel volume up as much as you want (even full out) then the master volume to taste. Once there, ALL the other amp models need to be adjusted (usually via their channel volume) to roughly match that Fender Amp (TOP 1). Then you have a relative comparative gain stage for the other 3 presets.
I usually run the Fender Gain very high, and the Fender Channel Volume full up for TOP 1 with Master Vol to taste.
I also have a POD 500 and run it the same as described above for the Fender Amp Model into my DT25 via L6 Link.
Give it a try, see what happens. Hope this helps you out a a bit?