It's a scam site. The URL is registered for only one year (i.e. from 2018-12-08 to 2019-12-08). Do you know of any legitimate business that only registers a domain name for one year?
The RCA outputs are line level outputs and therefore unable to drive a passive subwoofer. Those line level outputs would need to be fed to an external amplifier that drives the passive subwoofer.
It was back in 2004 when Intel switched from PGA to LGA. So that would be the Pentium 4 Gallatin, Socket 478.
You can get a Kaby Lake LGA socketed laptop like the CLEVO P870KM1/ SAGER NP9876.
The Pioneer VSX-D608 Owner's Manual says:
• Use speakers with a nominal impedance of 6Ω to 16Ω.
ELAC Debut B6
• Nominal impedance: 6Ω; minimum 6Ω
There's no problem.