Passive in wall JBL SubWoofer with Polk Rti4's

mlurbi
mlurbi Posts: 1
Setup:
Sony Amplifier: STR DG720
Front L & R: Polk RTi4
Front Center: Polk (in wall) TC615i
Surround: Polk (in wall) R65i
Subwoofer: JBL (passive in wall) HTI88 (has two 8'' woofers)

1. Should I use the wiring as per the JBL instructions? The Amplifier Front Right & Left speaker cables to Sub, then cables from sub got to the Front R & L speakers.

or

2. Or should I buy a second amplifier, then take the Subwoofer 'rca' type output from my amplifier, send it to a second amplifier and from there to the Sub?

Will it make a big difference? Is it a better way?

Note: I installed it in mode 1, and it seems like the sub is not very strong...

Thanks in advanced for your input.