You said that your speakers came with another receiver so I am guessing they are part of a HTIB system. Speakers in these systems are often the weakest link and are generally no where near as good as other speakers that are sold seperately. I bet that upgrading your speakers will have a dramatic effect on your sound. You need to get out and listen to some speakers. Depending on your budget, you might start by listening to Polk, Klipsch, Infinity, Boston Acoustic, Athena, JBL, Paradigm, Energy, PSB and Mirage to name a few. There are many others but these will be a good start. All these companies have speakers in many price ranges. The key is to get out and listen to a bunch of different speakers and choose the ones you like the best. Simple as that. A lot of people end up making it harder than it needs to be. Do look at reviews as they are a good source of info, but in the end go with your ears. Also, you might look at some of the online retailers. You won't be able to listen to them before buying but most online speaker companies have good 30 return polices. Some to look at are Rocket, Axiom, Nohr, Ascend and Swan. These are pretty popular. There is a ton of online info. on these companies as well as others.
Also, one thing to consider when looking at speakers. Try and stay with 8 ohm speakers. These are easier to drive. Your JVC is a decent receiver but it might have problems driving 6 or 4 ohm speakers. Now, if you want to upgrade your receiver? Hmmm?
BTW, what sub did you buy?
Shinerman