Amp questions

[SoundFreak]

As I near the completion of my basement I've decided after all the hard work I am going to treat myself to some nice HT seats and an AMP (assuming budget is within check, lol). Also, to add, I have yamaha V663 receiver and klipsch fronts, bose surrounds which I cannot wait to replace.

I'm not looking to spend a ton of money (under 500, preferably under 400) so what are some good options (if any)?

What are good, reliable, quality brands?

Will it improve my sound quality? Sometimes I get the feeling my speakers are underpowered. I think back to my car stereo days with the booming bass and when i added an amp, the sound was much more alive!!! I'm assuming this is true for this application too.

How are amps connected? Does HDMI go from the receiver to the amp or vice versa? Do I need anything else other than an extra cable?

Is it a worthy investment if I decided to spend the money or would I be better off upgrading to a more powerful receiver.