Assume a bi-wire or shotgun cable with a single connection at the amp end and two pairs at the speaker end. Assume a 100 watt stereo amp with a single set of binding posts for each channel. Does this amp deliver 100 watts to each of the separate cable runs.?
No it does not. It is not a straight 50/50 either. It can deliver anything from zero to full power through each cable. It is dependent on many variables including frequency and impedance.