in midi you should be able to do it just fine, but it depends on how you are set up.
if you are PC based then the PC would be the master and each ASR would slave to the PC on different ports.
alternatively, if you only have 1 port you can set the ASR's as slaves and use the first 8 midi channels for ASR1 and the next 8 midi channels for ASR2.
if you are using the ASRs with no external master, set ASR1 as the master, and ASR2 as the slave. Connet the midi out of ASR1 to the midi in of ASR2, then disable ASR1's 9-16 midi channels, and disable ASR1's 1-8 midi channels so that the one song sequence controls both boxes.
i've never done this with ASRs strictly speaking, but i've done it with other units in conjuntion with an ASR-x pro.
i dont use the song mode because i usaully just need the seqence mode the deal is I like every sound on different track and i hate all my drums on 1 track and i was trying to prevent from buying a MPC for my drums and sampling. because 8 is not enough!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!