I have a pair of Paradigm Monitor 3 V.2 High Def speakers for my front L&R home theater system. On speaker sounds very tinny with no bottom end. On inspection neither the main or tweeter loo

It sounds like the woofer part of the speaker is bad, while the tweeter is still good. You are going to have to replace the speaker. Speakers are generally sold in pairs, so it would be best to replace both rear speakers at the same time.

The Dolby curcuit in the Paradigm must be Dolby 7.1 or it will simply not be able to send the extra channel signals to the speakers. In otherwords you will not get the full 7.1 sound from two speakers added to a 5.1 amp.

Buy yourself some stand alone speakers, a base & two side speakers, they cheap these days, base speaker has buit in amplifier & plugs into mains, or get surround sound 5speakers & a base, again mains powered, loud enough to annoy neighbours on full. Built in monitor speakers are renowned feeble tinny sounds. Right click speaker icon, bottom right, on your desktop toolbar, open volume control, ensure volume sliders set to max.

THIS RECEIVER IS JUNK. I had the same problem with my receiver and Samsung gave me a new unit as it was under warranty. 8 months later the replacement which was brand new did the same thing. Samsung tells me it is my problem now. I should have demanded another unit. the best advice I have is not to buy this product. Samsung won't help you when it breaks and it will break. Nobody seems to know how to fix it.......

Your systemn is designed and built to perform 2.1 sound. If you want 5.1 sound you can do 2 things, connect another pair of speakers to the same speakerterminal as your front speakers, however this produces 5.1 stereo sound and not 5.1 surround sound.
You can buy a new system that has the proper connections.

This set will not have the proper decoding software to produce 5.1 surroundsound. sorry.

Sounds like it's just in 2 channel stereo mode, only 2 speakers working out of 5 and a sub, look for a selector switch for switching to 5.1 surround, as far as the no video problem try replacing the cable for the video connection. 

Nope RamaTheMan - you are incorrect! No way to get an actual surroundsound from your TV on this turd - this came straight from the Samsung FAQ -

"You cannot get surround sound from your television. On the other hand, if your television has audio output jacks you can connect your TV or Set Top Box to your Home Theater System and get stereo sound (that is, sound from the left and right speakers of your Home Theater System only).
To connect your TV or STB audio output jacks to your Home Theater System and get stereo sound, follow these steps:

1. Turn off your TV and Home Theater System.
2. Connect the Audio Out jacks on your TV to the External Audio Input jacks on the back of your Home Theater System. The External Audio Input connectors are typically labeled AUX IN. Note: There are usually two pairs of Audio Input jacks, AUX 1 and AUX 2. Each pair has a jack for the left audio input and the right audio input. Often, there are two Video AUX IN jacks as well. You can plug the audio cables into either audio AUX 1 or AUX 2. See the following diagram.
   

1. Turn on your TV and Home Theater System.
2. Press the Function Button on the front panel of your Home Theater System until the display on your Home Theater System shows AUX 1 or AUX 2.

For advanced installation, if you are using a High Def STB, you can connect an OPTICAL connection from the STB to the HTS. This is a specified cable that must be purchased separately.
In either instance, you must then set the HTS to its auxiliary input. (i.e AUX 1, AUX 2, DIGITAL IN) in order to get the sound from the HTS.
Note: If your television does not have Audio Out jacks, you may be able to get stereo sound by attaching the Audio Out jacks on your VCR to either the AUX 1 or AUX 2 audio inputs on your Home Theater System. If you attach your VCR to AUX 1 or AUX 2, you will have to tune your television to channel 3 or 4, and then tune to the station you want to watch on your VCR."

The "tiny sound" may be a blown woofer you are only getting sound from your high section.

It depends on what you want. Is your existing solution a surround sound system (You only mention a subwoofer, what other speakers do you have?)? Do you want full 5.1 or 7.1 surround sound? If you don't have this, and want it, your amp will have to be replaced, but your sub will fit in just fine. If you currently only have front left and right speakers, you will need to purchase a centre speaker and another pair (5.1) or two pairs (7.1) of speakers.