its actually a c.vega clsc 12s powered sub,
Your problem is that sub does not have an input sensitivity control, it is just on or off. Not good.
So you will have to see if your Pioneer receiver has enough output to keep the sub on at reasonable volumes.
So, this is what to do.
Go to multichannel in your set up menu of the Pioneer. Make sure you click sub yes, and set all your speakers to small and set the crossover to sub at 80 Hz.
the "SW Input Gain" setting within the "Multi Ch In Setup" menu. Here you can crank the sub output until there is enough output to keep the sub on.
Basically that is a lousy sub and not very useful and actually needs deep sixing to the recycling center. This is because when you set the sub output of your receiver to a reasonable volume it may not keep the sub on, unless you listen way too loud.
A preamp is potentially a solution, but I would can the sub and get a better one. That is the best solution if you can't find a volume that keeps the sub properly balanced with the rest of your system.