One of the more ridiculous techobabble things to come out of VOY. The crew can connect alien tech with barely any point of reference but it's own systems can't be adapted?
Yes, that was a bit dumb... still, we HAVE seen that in Season 5, episode 'Night', 7 and Paris tried rerouting power from the holodeck into the auxiliary systems... but failed because the hologrid was frozen.
I think its implied here that from Season 1 to Season 5, the crew managed to get the power from holodecks compatible with the rest of the ship (which is odd considering that fusion generators and M/AM is usually used for power generation on board.