When I bought the Bose Companion 5 setup I had never heard of SDR radio, but I bought a new computer just for radio stuff and since the Bose was sitting there from a previous computer, I plugged it in. Of course, it has pretty good sound, but the best part is the little "Control Pod" that comes with it. Could not be more perfect for SDR radio. You can touch the top to mute, in case something comes in on a different radio you want to hear. And the outside is a rubbery surface that's perfect ergonomically, you rotate the outside of the pod to control volume. I have it sitting right next to the mouse and I am constantly fiddling with it.
The Bose comes with a big subwoofer, which you may or may not want, I think you can get the same system without the sub for less money. But that little control pod really makes it perfect for SDR. I'd also be interested to hear from others what they're using for sound.
Below is my text from 6/1/2013 "New SDR CommRadio CR-1", page 28:
"I've been playing around with various audio solutions and have found what, for me at this time, is a great answer to all of my challenges. Best Buy closed their music department rooms in those stores which had them, now turning them into Samsung Experience rooms (to compete with the Apple stores). They had a fantastic sale during the last few days and I picked up several Roland CM-30 Cube monitors. They have a 6" diameter bass / midrange speaker and a smaller treble speaker, 30 W amplifier, numerous inputs and separate volume and tone controls for each channel. The thing is basically a mixer panel and a powered music/audiophile monitor in one package. I have all of my transceivers and both SW receivers hooked into it, and it has a separately controlled headphone out jack. It also makes a nice stand for the CR-1! It looks a bit disproportionate as a stand-alone setup, but when racked and stacked with my other stuff, fits just fine. Just my solution to my challenges."
In the year plus that I've been using this setup I've been pleased and have appreciated the flexibility the built-in mixer panel gives you with the various inputs. I did use two for a short while, but didn't find the second speaker to be of value since the source is monophonic. I just checked prices and the CM-30 seems to be selling at ~$219. from various sources. I hope this is of some help.
Not an easy question to answer - a lot depends on what you listen to most. I don't know anything about the FDM-S2 but I do have a selection of radios from scanners through a JRC NRD515 to Winradio 303. IMHO a speaker alone doesn't do the job, you can't tailor the response to suit what you are listening to.
I run all my receiver line outputs through a mixer with tone controls and then to a Sony amp and full range speakers. I can quickly adjust the sound to suit a broadcast band station and later to a ham sideband signal with intruding high audio frequency noises. It depends on whether you want 'quality' sound or 'communications' sound! Experiment until you find what suits you best. Speaker placing sometimes makes all the difference to intelligibility when digging a weak signal out of the noise - but then you should be wearing headphones anyway!
Good comments, I like the Roland powered speaker, might need to get one! Like a lot of things, this simple question about audio is more complicated that it seems at first. We can talk about 1) speakers, 2) audio controls ie: Woodbox Radio Tmate2 or the simple yet elegant Bose control pod and 3) audio mixers. Different people will like different speaker setups, Martin is exactly correct in making the distinction between "quality sound" and "communications sound".
With respect to one speaker vs. two speakers, put me down for two speakers with the FDM-S2. Each channel gives you left and right sound, yes it's mono in most cases. But in my brief time as an S2 owner there have been several times when I was feeding one signal to the left channel and something else to the right channel.
For me, besides having good sound, I would not want to control the volume with the mouse. I like having the volume control close and handy.
I also want a good set of speakers for my desktop computer for the Elad when it arrives. I have some bookshelf speakers I can use, but don't want to use a big receiver for them. My budget is a lot less, and I am thinking of either powered computer speakers, or a small amp for the bookshelf speakers.