Let's say for simplicity you go with the 2801. There is something called "2801 voice bundle" that will give you both the voice IOS, and a DSP module (PVDM2-8) good for 8 calls. If you need have 10 calls, order the upgrade that will give you PVDM2-16 instead.
Then for each router you need a module that is either VWIC-1MFT-E1 (older) or the newer VWIC2-1MFT-T1/E1 (newer, but both would work)
Check the PBX physical interface in case there is some cable that should be ordered from cisco (unlikely).
Your reseller should know all these things, if he does not, is not a good reseller.
With all the above you can support QSIG no problems. There are documents to facilitate the configuration for both routers and PBX. Once you have the routers on network and pinging each other, come back and we go from there.
Just to add to the previous info, you may need to use a feature called transparent common channel signalling, to connect the two PABX together. I have used it before to connect two sites together across IP when the end systems did not support IP only dpnss in the uk
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