Re: Speaker suggestions?
Keep in mind the speaker install will have more to do with SQ then the speaker you buy, the same goes for the HU, I am guessing the aftermarket HU was installed using and adapter harness, so all stock HU wiring, [speaker wiring, power and ground wiring] is being used.
If so, you are under-powering the HU, the stock 12V+ constant and ground lead can not supply the aftermarket HU with the current it needs, especially when the volume is turned up.
This needs to be fixed before you get new speakers.
The "fix", run a fused 12ga, [40A max] from the batt. pos.(+) to behind the HU, connect the HUs 12V+ constant, [yellow] to it, don't forget to cap off the stock 12V+ constant, [or depin the lead from the adapter harness if used].
Run a 12ga lead from the HUs chassis to the cars chassis, [dash subframe will work], if the HU is back braced to chassis ground, [stock rear support bar] as it should be, a 12ga ground is not needed, leave the stock wire ground in place. 94