Its all good man.....alot of these guys are going to give you **** without supplying any information.
They are correct when saying that most likely you haven't heard a properly installed Type R. A type R is pretty much in a completely different category than your Volf. Volfenhag is just a cheap brand kind of like legacy. Not saying that it doesn't work, but it is most of the time overrated on power ratings. A type R is simply just a better/tougher built driver.
I gave you a simple answer at first.....their is no way to get more power out of your amp with that sub.
honestly, people are going to give you crap about the sony amp, but it is alot better than your sub.
I would upgrade the sub before the amp.
If you would like to keep the sub and believe that it will take more power then their are plenty of cheap amps that would power it fine on a budget.
Check out
http://Profilecaraudio.com they have some amps on there for sale new and some refurbed.....but they are really cheap and you could get mono amp.
I think that they have a 400Wrms or so mono amp for under a 100bucks.
good luck with everything
and if you have any questions just post them without saying that your sub is better than others or you will most likely get flamed by most of the dudes on here.
curtis