Exactly what Audiobaun said, most 5 channel amps cut off at 500w @ 1ohm minimum for the subwoofer channel. .5ohm is also unrealistic for a "do everything" 5 channel amp.
5-channel car amplifier — 75 watts RMS x 4 at 4 ohms + 720 watts RMS x 1 at 2 ohms
That's the most powerful one that
Crutchfield sells @ 720 watts on the sub channel (2ohm)
The only 1 ohm stable one I see is the one I have which is listed here
Punch marine/powersports 5-channel amplifier — 75 watts RMS x 4 (4 ohms) + 500 watts RMS x 1 (1 ohm)
If you have questions about that one I've used it daily for over a year previously.
Like Audiobaun said, it's way more common to have 2 amps if you do speakers and a powerful subwoofer setup.