Joseph,
The way I (mis)understand it, you may:
1) Create a path (a rectangle or whatever) that covers everything and give it a grayscale gradient corresponding to the direction/kind and to the range of transparency (from full black to full white if you wish to go from full transparency to full opacity), so that the gradient corresponds to the transparency;
2) Select both the gradient path from 1) and the objects (group) and in the Transparency palette flyout click Make Opacity Mask with Invert Mask ticked or unticked, depending on which way you wish the transparency to go.
This should give your object a transparency transition across the whole group corresponding to the gradient (either way).