sub preformance decline w/ new amp

--95' oldsmobile*ninety-eight regency-- pioneer deh-2000mp (head)*hifonics 1610d 1600w*(2)kicker-cvr's(4-ohm)

i originally had this same set-up listed above but with a planetaudio 900vd 850w now with my old set up i could have the amp control all the way down, my volume at 43, and the subs would hit effectively.  I would then be able to turn my amp control to between 50 to 75% and have even more effect obviously. Now i replace the amp with a new hifionics amp and (2) new cvr's switched out and it does not hit as hard as before. So i adjust the bass eq on the amp a bit retry and it now hits harder then the old amp but i have to turn my amp control all the way up and volume at 46 to acheive this. i am very green to the scene but from the little i think i know i believe i just need minor adjustments to have it right. The (2) subs are wired for (4ohm). any and all is appreciated thanks

and the box is just like any standard box you would get at a shop or flea market for two twelves just a guess but around

4.5L x 2.5W x 2H give or take a bit

i read up on some resources and found the problem, i noticed certain notes were not being hit while others were and in reading i found it was my subsonic and phase that needed adjustment. a few secs of tuning with a jam on at the amp and all is gold problem solved. thanks

I dont think you realise just how important the proper box size is. 

they were the exact same, as i have learned more to audio and sound and checkin into my problem i found that the whole lost of preformance came from the battery and i have replaced it brand new. The amp works fine and really i think the box is sufficent although i am not educated on boxes size, ported or sealed wood or plexi etc. at the end of the day with the new set-up i get an extra 87.5 watts, if the hifonics is giving a true 550w @ 4-OHM, to each of the (2) twelves. i assume that is not a lot but i do see a significant increase in power hit and better tightness in quality sound to the bass.