I'd be interested to hear if anyone has been successful growing clematis under a lilac. Of the lilac we dug out, which were only three years old, the root mass was very thick and covered the entire area. I can't imagine much being able to compete with lilacs.

It can certainly be done......I have an entire garden area under a 60 y.o. lilac tree that I've been adding to over the years (initially this area was just lawn). I have two macropetalas growing up into mine, as I wanted the early season color before the lilac really leafs out well and blooms.

Kim, I'm not sure you need to be restricted to type 2's. For one, the bloom seasons will coincide to some extent so you may loose impact from either flower source. An earlier (type 1) or later (type 3) vine could provide extended interest. And I'm not sure I'd be overly concerned about pruning - of the vines I allow to ramble freely through larger shrubs like lilacs or small trees, I tend not to prune very regularly but only when they become too large or messy.

As to specific cultivar, I might lean towards a Jackmanii for length and profusion of the bloom season, intensity of color (and contrast with the wimpy lilac color), and the toughness/durability of the vine.