You can get connectors from Tracking World office for your HU, they are sold separately, I got these for my friend's Civic, 3000Rs only. And you will be able to connect extra monitors on the rear seats. It supports 5.1 channel surround sound. The sound quality is not that good but what do you expect from a stock pre?
Speaker level input is not that good, I am sure you're talking about they pioneer device. It adds a lot of noise in your music, I would suggest to buy connectors and use an amp. But if you need to compromise on quality then its your call to use speaker to RCA connectors they only cost 200Rs.