Eric has mentioned Reger's Problems to combine traditional sonata form (in a very schematic way) with Wagnerian harmonic language. Reger was a good composer, of course, a great master of variation, fugue and choral fantasy, but his use of sonata form I would compare with a vase in which water is filled, and not with a river making its way through the landscape (as I would characterise Bruckner's much different schematism).
Regarding this, it's remarkable that Hausegger's Nature Symphony contains no sonata form movements. Wagner's idea of organic motivic development and endless melody unifies the work even without using sonata models.
