your HU has only 1 preout. if you use that preout for subwoofer you wont be able to connect speakers via amp.
Solution for you is to get these wires. I am using it in my car.
are you planning to put speakers with amplifier too or just subwoofer?
For sub you can go for rockford , infinity or kicker for good sound quality.
I got my infinity 1260w for 5.5k.
A good 4 ch amplifier will cost you 10k or less and if you are planning for monoamp the basic ones starts from 10k or more. you can go for JBLGTO series , Focal , kicker , rockford. all are good brands. I wont prefer sony and pioneer for anything as i had bad experience in past with their products. They are just loud not clear.