[boost] [Accumulators]multiple statistic instances

I am trying to create an IIR filter (see e.g., http://en.wikipedia.org/wiki/IIR) using the delay buffer implementation recently discussed. To do this I need two delay buffers for my filter, one for the samples and one for the computed outputs. I have tried templating my delay buffer with a discrimating type, but I can't get more than one buffer instantiated. ie the following creates only one buffer instantation. accumulator_set<int, stats< tag::delay<>, tag::delay<my_other_delay> > > acc( tag::delay<>::cache_size = 3, tag::delay<my_other_delay>::cache_size = 4 ); Is this worth perservering with? any hints? or would it be better to wait for the next version of accumulators?