How do I know if I need an amp?


My system is as follows:

Marantz SR8200 AV Receiver
Totem Mites bookshelf speakers
Totem storm subwoofer
Onkyo DX-C330 Analog ouput disc changer

I've got the speakers wired directly into the sub and treat the bookshelfs and sub as "large main, left and right" in the receiver's output setup.

My living room is quite small, I listen to the system from about 8 feet away on the couch.

What kind of changes to listening quality could I expect from buying an amplifier for the system at this stage? I don't plan on buying new speakers anytime soon, so I am more interested in the incremental clarity that I could achieve over a need for any additional power.

I'm not an avid movie watcher, so I wonder if a 2 channel amp would make more sense, though the marantz PM5003 I saw ($600 is about my price range) only puts out 40watts, whereas my speakers are rated up to 80 watts, and the receiver I have now puts out 120watts.

Is there a big quality difference between the SR8200's 120w per channel and a stand alone amplifier's 40watts? Would a 120w amp, used in a stereo set up, make a big difference?

Thanks
manbehindthcurtain
Unless your planning to do separates, that is a preamplifier and amplifier what you may be looking for is an integrated amp. That is a receiver minus the radio.
Ratings of watts of a speaker are more a guide as to how much to limit yourself to. Will playing a 40 watt amplier loud equal a 120 watt played lower? Maybe. How loud do you listen to music? Are we talking rock concert levels or maybe chamber music levels? More power is more power but is it needed is something you have to ask. Just how loud do you want that crescendo to be? How dynamic do you want things. Maybe the best bet would be to see what a 40 watt amp sounded like in your system and go from there. A good audio store might let you have one on a demo to find out.
I would get an amp - it would improve the sound noticeably - but I would go with a different one than the Marantz PM5003. By the way, you can get one for $449 on amazon.com

I would consider getting it used here at the audiogon.com
You will end up with more quality for the buck.

Take a look at these :

http://www.audiogon.com/cgi-bin/cls.pl?intatran&1256328090&/Onkyo-A-9555

http://www.audiogon.com/cgi-bin/cls.pl?intatran&1256065250&/Music-Hall-a25.2

http://cgi.ebay.com/Acurus-DIA-100-direct-input-integrated-amp-NO-RESERVE_W0QQitemZ180385071434QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item29ffc9c14a&_trksid=p3286.c0.m14

These have more power than the Marantz, and would sound better in my humble opinion. I would recommend the Acurus especially.

Your ears will thank you if you upgrade the amp...

Another possibility is going with adcom saperates.

http://cgi.ebay.com/ADCOM-GTP-500-II-Stereo-Pre-Amplifier-Tuner-Preamplifie_W0QQitemZ200375882470QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2ea75552e6&_trksid=p3286.c0.m14

http://shop.ebay.com/i.html?_nkw=adcom+amplifier+555&_sacat=0&_trksid=p3286.m270.l1313&_dmpt=Vintage_Electronics_R2&_odkw=adcom+amplifier&_osacat=0

These will give you plenty of power - 200 watts per channel.