How do I know if I need an amp?

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.

Thanks for the amp recommendations. A question about installation and setup-

Right now, I am using my receiver inputs for my digital cable and dvd player for surround sound. If I bought, say the Acurus DIA 100 amp, or any other stereo amp, would I be able to run the amp to the CD player, and still maintain my surround sound and stereo output for my DVD and Cable?

given that you have a two channel set-up, i'm not sure why you need surround sound--it seems to me that you should be listening to each source in (2ch) stereo. that being said, i concur with the foregoing that you'd be better served by ditching the avr and going to either an integrated or remote-controllabe seperates such as the above-recommended adcoms. you would then connect all your sources--cable, dvd, cd--directly to your integrated or preamp.

when You ask "when"...it is clear what you currently own,is
failing to satisfy, otherwise, the thought would never enter
your mind."The bloom is off the rose"?IMHO that is.

Love Your Music!

Why do you think ditching the capability for surround sound is a good idea? Because I am treating the bookshelfs and sub as mains together?

Ultimately I would like to move towards a home theater setup that will also do stereo. I understand though that the bass on the Mites is limited. I'm starting to feel like getting the Mites was a mistake, because theyre too nice to relegate to surrounds, but not big enough to power stereo listening.

Would something like the Marantz MM8003 provide a bridge to future growth in a home theater setup, but still provide power for the mock "surround" setup I have now?

Bob, Can you explain what you mean by "high passing" the Mites (from an execution stand point). I assume you mean to reduce the frequency levels they play - can this be done via my receiver?

I am gathering you recommend that I hook the sub directly up to the receiver as a "sub", and do the same with the fronts. How do I "high pass" the mites?

I want to also thank everyone for their help. I have a lot of fun with this, there is so much to learn, and this site is a great resource especially for us newbies. Thanks!

What cables are you using ?

If you are using thin ones that came with the receiver, you might want to upgrade the cables first - and then see if you like what you are hearing.

You can get Ixos gamma RCA cables and Ixos gamma speaker cables at accessories4less.com That's what I use, and I like them. They got good reviews on hifi magazines.

http://cgi.ebay.com/Sensational-IXOS-Gamma-1002-Encore-Audio-Cable-2-Meter_W0QQitemZ140337596201QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item20acc5c729&_trksid=p3286.c0.m14

Also, you can add this inexpensive power surge protector - improves the sound, and protects your electric gears :

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370249463085&ssPageName=STRK:MEWAX:IT

Your present setup is not bad - should sound pretty good, with the right cables.

I would go with a different amp than the MM8003 - there are better sounding ones out there for the same money.

I just listen to 2 channel set up even for movies - I don't miss other speakers. Since you are trying to improve the sound of music, I would consider getting the adcom preamp and adcom power amp.

They would improve the sound in a noticeable way. Also, the culprit might be your source - amp can't improve the sound a lot if the source is not good.

I would upgrade the wires (if you haven't already), then the CD player (or DVD/CD player), and then add a 2 channel adcom amps to your Marantz SR8200 for the fronts.

You can connect the adcoms to your present Marantz receiver, to power the fronts. That would be better than getting MM8003 - I would consider other brands than Marantz.

http://www.accessories4less.com/make-a-store/item/IXOSXHS606S/IXOS/XHS606-15-AWG-GAMMA-GEOMETRY-SPEAKER-WIRE-SILVER-PER-FOOT/1.html

http://www.accessories4less.com/make-a-store/item/IXOSXHA5162M/IXOS/XHA516-PC-OFC-Gamma-Geometry-Audio-Cable-2m/1.html