The 9831 has 4v preouts, along with Bass Engine Plus and a slightly different look.
Crutchfield is your friend...
CDA-9831
http://www.crutchfield.com/S-dfFDxIj8C56/cgi-bin/ProdView.asp?g=300&tab=essential_info&i=500CDA9831#Tab
» detachable, fold-down face
»
variable button color
» plays MP3 and WMA files
» plays audio CDs, CD-Rs and CD-RWs
» MaxTune SQ tuner
» 12 FM/6 AM presets
»
Bass Engine Plus (bass center frequency, width, and level, plus treble center frequency and level adjustments, as well as 4-channel digital time alignment and a 3-position, 12dB/octave crossover, subwoofer level and phase control)
»
MediaXpander (restores clarity and detail to compressed or broadcast audio)
» source tone memory
» iPersonalize setup options
» XM and SIRIUS Satellite Radio controls
» CD changer controls for Alpine Ai-NET changers only
» optional auxiliary input
»
4-volt front, rear and subwoofer preamp outputs
» MOSFET internal amp
» clock
» wireless remote
» 18 watts RMS/50 peak x 4 channels (CEA-2006 Compliant)
» CD frequency response 5-20,000 Hz
» CD signal-to-noise ratio 105 dB
» FM sensitivity 9.3 dBf
» warranty: 1 year
CDA-9851
http://www.crutchfield.com/S-dfFDxIj8C56/cgi-bin/ProdView.asp?g=300&tab=essential_info&i=500cda9851#Tab
» CD receiver with built-in amplifier (18 watts RMS/50 peak x 4 channels; CEA-2006 compliant)
» motorized, detachable, fold-down face
» plays audio CDs, CD-Rs and CD-RWs including discs burned with MP3 and WMA files
» Bass Engine (bass center frequency, width, and level, plus treble center frequency and level adjustments)
» BBE sound processing
» source tone memory
» XM and SIRIUS Satellite Radio-ready (you can add satellite radio for under $100, plus subscription)
» compatible with Alpine's iPod interface adapter
» CD changer controls for Alpine Ai-NET changers only
» optional auxiliary input (adapter required)
» front, rear and subwoofer preamp outputs
» MaxTune tuner
» 12 FM/6 AM presets
» clock
» wireless remote
» CD frequency response: 5-20,000 Hz
» CD signal-to-noise ratio: 105 dB
» FM sensitivity: 9.3 dBf
» warranty: 1 year