To start, if you amp is not rated for 1 ohm opperation, then you are damaging your amp.
This is probably the case, since your thermal protection keeps shutting off your amp.
You may end up damaging your speakers permanently as well too.
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The main benefit with a parallel circuit is more power, if your amp can put it out. Parallel is better for bass. The main con is the stress on the amp.
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Series results in less power, but puts less stress on the amp. Series circuits are more suited for higher frequency ranges.
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My suggestions to you are;
1) run each of your 6.5" speakers on a seperate channel of a 4 channel amp, providing
75W/channel.
or
2) get a 2 channel providing 150W per channel, and run two speakers in series on each channel of the amp.
Both suggestions will give you 100W of power and won't over stress an amp.
