Yes, you can fix music system with woofer and amplifier after the purchase of the car. But it is recommended that one should buy and install the accessories only from Hyundai Showroom. The service station provides better insulation and uses good quality of wire.
That's great if you are planning for a new car. It might interest you to know that Hyundai is planning to launch the facelift version of the Grand i10 sometime this year around August/September. The Grand i10 facelift is also likely to get AMT (Automated Manual Transmission). So if you are planning in 1-2 months, we suggest you to wait for its new facelift version and other new upcoming cars.