Guys. Can you check this setup if it is right. My vehicle is a Toyota Revo

Head unit - Alpine CTA 1502
Front Speakers - MB Quart 325.02
Rear Speakers - Stock
Front Amplifier - Alpine 3544
Rear Amplifier - None, connected directly to the head unit

Basically, the output sound of the MBquart is not balanced. My bro suggest that I change the front amplifier to an amplifier with crossover control AND accepts 4-volt output from the HU. can you recommend me one. budget in mind is below 5T.

second. I was thinking of installing a subwoofer. can you recommend one? Ideally, I want a sub that is not space consuming and its purpose is just to have the low freq go there. amp to be used is Majestic 250X2. (It was cionnected to the MB Quarts but rewired it for Sub Use)