"a google search turned up that this 400 to 800 cables do not supply enough power for the imac to recognize some devices. what do I need to resolve this issue?"
Does the Alesis have a power-in port for an external power source (i.e., a "power brick")?
They can be bought very cheaply on ebay.
That will solve your problem.
Does the Alesis have a power-in port for an external power source (i.e., a "power brick")?
They can be bought very cheaply on ebay.
That will solve your problem.