A couple other things to consider.

1. If your new speakers are 4 ohms they are getting less power from the amplifier because the factory speakers are 2ohms.

2. The new speakers my have a lower sensitivity than the factory speaker which, even if they were 2ohms will take more power for a given "sound level".

About 5 years ago one of the factory speaker blew in my GMC Envoy which has the Bose system with 2ohm speakers. I couldn't find any aftermarket 2ohm speakers in my budget range so I shopped by sensitivity and found the Infinity Reference Series to be the most efficient in my price range. I still needed to run the volume setting a little higher than I did with the stock speakers but it was an improvement.

One way to punch up the midrange without a midrange adjustment on the head unit is to lower the highs and lows a bit.

Another thing I've experienced after a speaker change is it take a while to fiddle with the equalizer settings until things sound right. After a couple weeks of tinkering, I usually get it right and am happy.

Tom