If you have cash on hand the sequence of your buying should be
Recomendation for buliding a good quality setup slowly and not to keep changing them in the future for a better one as you accumulate your budget as months go by..
step 1. headunit not lower than 10k-35k depend sa level ng quality habol mo recomended decent headunit 13k-20k
(Brand- Pioneer/ Alpine/ Panasonic/ JVC /Sony)
And if you have sufficient money left.......
Step2. is to buy a good front speakers (2way seps preferrably 3way) not lower than 9k- 35k should at least 75-125w power handling depende sa level hanap mo. Recomended for a decent seps around 12k-17k(2way).
(Brand- Boston/ Infinity/ Focal/ Dyne Audio/ MB Quart/ JBL/ JL Audio/ DLS/ Diamond Audio)
After a few months if you have more money........
Step3. Buy a good amp 1pc 4ch. around 10k to 30k around at least 75w- 150w per channel recomended front power 100-120w class A/B Recomended price for a decent amp would be 16k-22k at least (60w x 4ch).
(Brand- Kicker/ Rockford/ JL Audio/ DLS/ PPI / Audison/ X-tant)
Step4. Buy a good sub 1pc to 2pc Total budget around 5k-25k 1pc or 2pc depend on price. power handling around 100-400w per pc. Recomended budget for sub 100-150w per pc. Recomended price for decent sub would be 8k to 15k at 250w per pc.
(Brand- Kicker/ Boston/ Rockford/ JL Audio/ JBL Soundstream)
Step5. Buy a 2nd amp for your sub if needed and use your existing amp to power your front and rear or front only at higher wattage (80w-125w seps). Budget for sub amp 16-35k 250w to 500w per channel or mono channel. Recomended good quality sub amp price 23k-30k preferrably same brand as your existing amp. recomended decent power at 500w mono if you decide for buy a 2nd sub or 300 w if using only the existing sub.
Step6. Buy a good sound processor or EQ at least 20 band or 10 band parametric best is 30band . Price range recomended around 10-16k.
(brand- Audio Control / Rockford/ PPI/ Autotek)