Hi Zach,
A speaker doesn't use all the voltage/current (power) that is available from an amplifier unless you turn up its volume conrtol. In theory, a speaker that is connected between 2 amplifiers like that (the amplifiers are bridged, and the speaker is their bridge-tied-load) can draw up to 4 times the normal power from the amp and therefore cause it to blow-up!
Just use common sense and keep the volume no more than it was with the speaker connected normally.
Use your ears, not just the position of the volume control. A volume control that is turned to half-way does not necessarily make the amp produce half-power. It could be a lot more or a lot less.
I bet your stereo says, "Minimum load impedance is 3 ohms". Then it can safely drive 2 paralleled 8 ohm speakers, but will get pretty hot when played loud.
My stereo says, "High Dynamic Power", which reads good, but actually means that it has a weak power supply that can give massive power but only for a moment until its voltage sags. That used to be called 'Music Power".
It also says, "Low Impedance Drive Capability", which is true. Its rated power into 4 ohms is about 1.5 times its rated power into 8 ohms. But its rated power into 2 ohms is the same as with 4 ohms so that's when its power supply is really straining. Who cares, it sounds great!