ASIO = ONE device driver at ONE time.
Thats the way its spec'ed.
You can have multiple interfaces IF they're running under ONE driver (for example, I can daisy-chain two more Motu interfaces on my Motu828mkII to make 90 i/os because they run under ONE ASIO driver.)
Additionally, if you dont have the interfaces locked together with a time clock, they will drift over time as the crystal clocks beat buried in each one beat at slightly different rates as no crystals are ever exactly the same.
If you want more i/o, save your pennies and get a bigger interface.
Cobbling multiple interfaces rarely works or works PROPERLY.