In order to use multiple modules you need to make sure that all of the SCXI modules are in multiplexed mode and NOT parallel mode. This will cause all of the channels on the SCXI 1520s to be multiplexed to channel 0 on the PXI 6070E.
You then can scan any channel you want by using the SCXI channel string ob0!sc1!mdx!y, where x is the module number starting with 1, y is the channel number for that specific module. Your scan list needs to scan all of the desired channels on module A in order, before scanning the channels on module B.
You can open up MAX or most LV examples and enter (assuming A is md1 and B is md2) "ob0!sc1!md1!0:1,ob0!sc1!md2!0:1". However, I would recommend using virtual channels and just separate them with commas. Make sure you put them i
n the correct order as well.
I hope this helps.
Joshua