Problems with gps

[Sabatino]

Hi all;
I am an happy owner of Oregon 550t and I would like to know which method or guide to follow to visualize on the gps more independent tracks pieces simultaneously and together with the preloaded map.
The problem is that if I load these tracks pieces as a single track (since in this gps is not possible to view more tracks at the same time), all the final parts of the pieces are connected with the beginning of the following piece making the vision very difficult.
For this reason I would like to to convert the track to a map and then import it in the gps and put on top of the preloaded map.
As an alternative i could first download the preloaded map from the gps to the pc, insert the track and import everything again.
Note that is not important that the gps follow this track, It could only show it for example like a river; I don't need any navigation function but only see the track with no connecting lines between the pieces.
Does someone of you know the procedure to do this as simple as possible?
All what I have now are hundreds of tracks in .plt or .gpx format not joined and tens of km one far from the other; I must visualize all of them and togheter with the preloaded map.
Thank you for every suggestion.