Passive subwoofer...huh???

Ok, I am a dufus. I just bought an RBH VDS-10A passive subwoofer on eBay. I have a decent system; Threshold Forte Model 3A amp (200 wpc into 8 ohms); KEF Reference 103/4 loudspeakers; Parasound PLD-1100 preamp & Arcam Alpha 8SE CD player. Sounds fantastic, with the KEFs just a tad weak in the bass department. Didn't want a powered sub (too much like home theater, I thought), so I saw the RBH passive sub with its nifty 10" aluminum cone driver and said "Eureka." Naturally I bought it. No thinking, just bought it. Then it occurred to me; can I power it directly from my amp, or do I need a dedicated subwoofer amp??? If I drive it directly from my amp, should I run right and left channels into it (it only has one set of 5-way binding posts on the rear), or should I just run one channel?? Have I totally wasted my money?? I'm assuming the sub has an internal "crossover" to limit high frequency input, but I don't know that either. Doh!!! Help guys. -David (should be "KefKing" & not "Klipschking")
NHT makes a couple of nice little sub amps that are stand-alone units with adjustable volume, crossover etc. which would make your connections really easy. Try Ebay if not here on Agon
I also recommend the Reckhorn A-401 amplifier for your subwoofer. An excellent amp with many adjustments for fine-tuning. Details at
Specs from their site:

System Type: Non-powered Subwoofer
Frequency Response: 30Hz-200Hz (±3dB)
Sensitivity: 87dB (2.83V @ 1 Meter)
Recommended Power: 100 - 200 Watts
Drive Units: (1) 10" (254mm) Aluminum Cone Subwoofer
Crossover Frequency: N/A
Crossover: N/A
Impedance: 4 Ohms
Cabinet Material: Medium Density Fiberboard (MDF)
Cabinet Finish: Black Oak Woodgrain
Dimensions: 14-3/4" H x 14" W x 16-1/4" D
(375mm H x 356mm W x 413mm D)
Weight: 38lbs (17.24kg)
Warranty: 5 years

You need a crossover and might as well get a separate amp.
Thanks all! I have taken your advice and I'm looking at either a Reckhorn or an NHT dedicated subwoofer amp... should be pretty tight when I'm done.