I am attempting to figure out what type of system I can actually put in my '70 Mustang. I would really appreciate some advice as I've no clue. My goal is to create a system for moderate listening; not for excessive volume. I'd like to DIY the install as much as possible but I'm going to need professional help with the speakers since I'm figuring I'll need custom kick panels in the front.

The options for speaker locations are very poor. The car originally had one mono speaker in the middle of the dash. No other speakers in the front. The rear had 2 6x9's on the rear deck but I've added a fold down seat option to allow for an enclosure if necessary. All the speakers will be replaced but due to space limitations, they will tend to a smaller footprint side.

I would like to install a subwoofer but am looking for cleaner sound as opposed to massive bass.

As to amp(s), I have a chance to pick up a Helix amp while in Paris but don't know which one I need or if I need one or two. The only head unit will be an Empeg with a tuner module. The main reason I'm considering Helix is feedback in the forum and small size. The options are:

http://www.audiotec-fischer.com/brax_helix/english/helix/performance_line/verstaerker/hxa20x.html
http://www.audiotec-fischer.com/brax_helix/english/helix/performance_line/verstaerker/hxa40x.html
http://www.audiotec-fischer.com/brax_helix/english/helix/precision_line/verstaerker/hxa400.html

Any advice would be greatly appreciated. Also if anyone knows of good installer in the Pittsburgh area, I'd could use a recommendation.