Do I need a subwoofer? Which brand and model?

"12-02-14: Stringreen
You don't have to spend that much....subs are not that critical."

Not for you. lol. But the OP doesn't have a pair of Vandersteen 5's.

I need to add the following observations on my situation and ask a few more questions. I am testing a variety of music on my current setup and my observation is that the bass drivers on my speakers are hardly being driven, even with bass heavy punchy songs. I tried to turn the volume up to see the effect that had - the other drivers reacted a lot more than the bass driver. Turning the bass control on the amp increased the bass but not in a satisfactory way - the sound was muffled.

First - I would like to ask (apologies if this is getting repetitive) if this is due to the amplifier- to remind everyone, this is a NAD C375BEE integrated amplifier, at 80W per channel.

Second - my Wharfdale EVO 50s continue to satisfy me at the high end but are practically non-existent at the lower end. Is this a speaker issue? Does anyone have experience with these particular speakers? Should I consider replacing the speakers to get the full sound I seek?

Third - if this is an amp issue and adding a power amplifier to this setup and using my integrated as a preamp is the way to go, can I go with a NAD C275BEE, which is a power amp at 150W per channel? Will that be good enough or do I need to go higher such as a NAD M series? How high should I go to see a distinct difference in the fullness of the sound I want?

Make absolutely sure that you have your speaker cables connected in phase.

Also make sure that your Oppo is set up to play in 2 channel mode, and not something else like 5 channels.

Try removing the jumpers on the back of your NAD and run interconnects from the output on your Oppo going directly into the amp section of the NAD. Listen to the system and use the volume control on the Oppo.

ZD ....Pullllese.....My speakers are 5A's.....enough jest. Richard and I spoke at length about subs, and for the vast number of 5.1 systems, almost any sub (a couple of hundred dollars worth) is fine. Yes, subs are valuable in that they allow the regular speakers and amps to work without that extra load of lows. I have a separate 5.1 system in a different room than my "big" system. It is a Denon AVR X3100 with NHT floor standing speakers...with zone 2 connected to two speakers in every room of the house. It can show me what speakers are working, and generally, unless I am showing a movie with colliding railway trains, or bombs, the sub Isn't even working. (control is by Audyssy (spelling??). My sub is an Outlaw Audio set in a corner of the room, and it can shake the house when those bombs explode...and my room is quite large

A better amp will do very little to fill that room. Find the best sub you can for the money and then get another. Learn all you can about eq's, room correction and time delay.