Did you get a manual with it? According to the Sony site this speaker originates in Sony MHC-GX450.
"This product bundle includes the following models:
HCD-GX450 - STEREO MINI SYSTEM
RM-SC3 - REMOTE CONTROL for Shelf Mini Systems
SSRG444 - FRONT SPEAKER FOR MHCGX450
SS-WG450 - SUBWOOFER FOR MHCGX450"
Find the manual here and learn a bit about your seprated sub...
See page 7.
As can be seen, the subwoofer has two connections to the mothership, very unlike the standard speaker level (+/-) speaker wire or RCA-Line-Level subwoofer out that 'normal passive or active subwoofers use, respectively.
Not knowing which of those your unspecified Pioneer receiver supports, it is impossible to say. Does your Pioneer have that control jack?
Mini-systems are generally not designed to be pieced out and used with grown-up gear. The absence of standardized connections is the clue.