Those are not an upgrade - they are a waste of your money for something that is really not worth mentioning.
They are the steal they appear to be - but not the way you think they are.
That is - they will be happy to steal your money and give you a very cheap, not so great product.
Why not try something like this if you can swing it:
http://www.jr.com/JRProductPage.process?Product_Id=4007837&JRSource=google.datafeed.ONK+HTS770B-RB
or here:
http://www.ecost.com/ecost/shop/detail~dpno~474173~Action~Detail.asp
Read the specs on the HT-S770 system... Instead of 9 watts * 5 plus a 12 watt sub, this is 130 watts * 6 plus a 220 watt sub.
Instead of a 4" sub, it has a 10" sub.
Instead of 10% THD - try .08%
Instead of a total weight that's probably 10 pounds, this comes in a box that weighs about 70 pounds.
It is very serious and a great deal for the price. Far, FAR superior to what you are looking at right now.
Don't waste your money on some half baked upgrade when you can save it for a few more months and get something that will really blow away what you have now. You really won't be sorry you did.