Seconding Mechans' comment, when the two amplifiers are paralleled, to the extent that each of them is "trying" to put out a signal that is not absolutely identical to the signal that the other amp is "trying" to put out they will each be forced to drive that difference into a load impedance corresponding to the output impedance of the other amp. In the case of most solid state amps that output impedance will be very close to zero ohms.
It looks like the HMA-7500 can be bridged. However in this case I would not recommend doing that either, because the impedance of the LS50 gets as low as 4 ohms at some frequencies in the bass region, where a lot of energy is often required. In bridged mode the amp will "see" a load impedance equal to 1/2 of the speaker's impedance, meaning as little as 2 ohms at some frequencies. The HMA-7500 is not rated to drive less than 8 ohms in bridged mode.
Regards,
-- Al
It looks like the HMA-7500 can be bridged. However in this case I would not recommend doing that either, because the impedance of the LS50 gets as low as 4 ohms at some frequencies in the bass region, where a lot of energy is often required. In bridged mode the amp will "see" a load impedance equal to 1/2 of the speaker's impedance, meaning as little as 2 ohms at some frequencies. The HMA-7500 is not rated to drive less than 8 ohms in bridged mode.
Regards,
-- Al