Have you looked into having the 1400 amps repaired? Running the PT800/PS1400 in a stacked setup, using the built-in 130 htz xo will provide the best "full range" speaker.
Alternately, using other plate amps for the 1400s, or using completely different subs, with the 800s sitting on top, with the AVR's xo @ 80 htz is almost as good, depending on the musical quality of the sub. Or sending a full range signal to the plate amp speaker line inputs and using the speaker line outs to the 800.
I've done this using a pair of diy subs, using JBL SUB1500 drivers and BASH plate amps. Similar to Mike's sub1500 setup