Yes, you can use a bigger sub. In a small room a 100W sub is enough.
If you want to find a cheap Panasonic surround sound system, you can check websites like eBay and Amazon. You will find systems at amazing prices, and even sometimes with free shipping.
You can certainly use any subwoofer that has its own amplifier with your surround sound system, if the only signal you send it is the sub line out from the receiver. The power rating of the subwoofer gives you a good indication of the volume balance that you can expect. If you have a 5.1 receiver that is rated at 400 watts total power, your subwoofer should have a power rating of at least half of that for itself.
A good surround sound system can be bought from bestbuy or bestbuy.com. They offer great, cheap warantees on their products. In addition, they will install it and you can call the Geek Squad with questions.
I assume you are talking about a surround sound system, they have the cheap ones at walmart for about 100 dollars. They just get more expensive from there though.
Cheap home surround systems can be found at most electronics retailers. Walmart, Best Buy, HH Gregg, Target, and KMart all have several brands to choose from.
Cheap speakers can be purchased on eBay. Depending on the seller, you can find some cheap speakers. On this store, the items may be super cheap but you might have to bid for it.
Monoprice and Vizio offer cheap surround sound systems that get good ratings. Pioneer and Sonos also manufacture surround sound systems at the lower end of the price range.
Tub surround may come in cheap or expensive prices. But why purchase expensive ones when you can purchase a cheap one in a good quality. All you have to do is visit Nextag and look for the cheapest tub surround they offer with a good quality.
the Samsung HT-D550 is a good cheap system.
A cheap gps system would be one that only gives you routes to the place you are looking for. Price wise any gps system under one hundred dollars is considered cheap.
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Prices on surround sound systems vary. You can find a cheap one for right around $100 bucks. To get anything of quality you will usually spend right around $500-%1000 and up. Surround sound is like anything else you get what you pay for. Panasonic and Pioneer make some great entry level sets.