Ardour + Jamin.
i use Jamin with ardour as an insert in the master postfader. Jamin takes around 95% cpu usage and an export needs from 2 to 40! Minutes.
The system specs are:
Jack 0.116.1 (checked other versions but without a solution)
Archlinux with 2.6.28 stockkernel
cpu x86_64 Amd dualcore.