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Your stock speakers won't handle the same wattage as the tubes. If you want to run an amp to them, you'll have to change them out as most stock speakers can only handle about 35 watts RMS at most. You'll need a 4 channel amp for your new replacement speakers (front and rear) and a 2-channel amp for the tubes.
Never go by max watts, ALWAYS go by RMS watts as these are the watts the amp will provide continuously.
You'll need to match the RMS watts of each tube to each channel of a 2-channel amp at the same ohm rating.
If your subs are 150 watts RMS @ 4 ohms each then get a 150 watt RMS X 2 @ 4 ohm amp.
A two channel amp is kind of like two amps in one. Each channel will provide a connection to a sub or "collection" of subs as long as the impedance (ohms) doesn't fall below the rating of the amp.
Bridging is combining channels of usully no more than two channels of an amp. Bridging an amp is determined if an amp can be bridged and by how the subs are wired to it. Most 2-channel amps can be bridged to one as well as most 4-channels can be bridged to 2-channels. Some amps can be wired for many different channels as well.
ALWAYS refer to the user manual BEFORE attempting to bridge an amp.
Source(s):
25 year electronics technician, audio guru