Has anybody tried using single solid core cables?

Tried them went back to my STEALTH V14 much better detail.

I am currently using solid core wires only. Of all the cables tried, they seem to follow along the tunes better. When it comes to wire design IMO less is always more. It is not uncommon for Hi-Enders to try a variety of cables within the same price range only to find the sound to be different and not necessarily better. Wire companies know that only too well, and they excell at selling different sounds and not necessarily better.
As for me, I try to focus on simple designs coupled with high quality cables, the little known Shishido silver and copper. All single wire (as opposed to multi wire, solid core which IMO is tantamount to stranded wire). The sound is dense and musical, sweet and organic without being sirupy or veiled whatsoever. I wouldn't dare venturing again in that maze of solid vs hollow ribbon vs geometric etc. etc.

Since my earlier post about using all solid core, I did a tweak. Brass conducts less effectively than copper, and I so I took my cheap banana plugs out of the loop. I also used DeOxit on all of the connections. I'm getting better highs now.

On using romex or "HomeDepot" wire, there is a drawback. Larger gauge copper has skin effect, and the wire will also oxidize quickly compared to OFC.

I concur on removing the terminations. My Mapleshade Double Helix are simply bare wire and sound all the better for it. I've read on other sites where some have removed the terminations on their Anti-Cables for better sound.

As for gauge, the Mapleshades are around 18 ga which seems to hit a sweet spot of sorts. Works like a charm.

All the best,
Nonoise

I'd like to add my 2 cents to the long list of responses above, pertaining to solid core cables vs. "whatever".  I have a considerable collection of interconnects and speaker cables of all lengths, aquired over the past 50 years. All of them, different designs, based upon bundles of stranded copper and silver plated wires, and almost every concept of insulation, isolation and shielding imaginable.
That said; - - -  along the way, (about 20 years ago) I stumbled into an ad in Stereophile (I think) for a small private company in Florida who was making and marketing Solid core, twisted pair, enameled high purity copper speaker cables, terminated with your choice of quality bananas or spades. The thing that caught my eye was the price. At that point in time I was using 15' speaker cables (due to routing requirements). I called the owner and he said he could make me a pair with bananas and ship them out same day. He even said that I could ship them back for a refund if I didn't like them. And the price was $25.00 for a pair. MY God, how could I not check them out.
When they arrived I just about sh _ _ my pants!! They were so stiff, he might as well used 1/4" copper tubing. Insane ! It never dawned on me that they would be that gnarley. With the way my system was set up at the time there was no way I could use them. Wasn't worth sending them back. So I just coiled them up; - - put them in a box and stored with the rest of my "collection":.
Next encounter ! - - - - about 7 years ago, I ran into a person at an audio show, who said he was a officer of the Chicago Engineering Society. He had in his hand some bold looking (RED) interconnects with VAMPIRE RCA's. We talked about his theory and experiences while developing these cables. Once again they were constructed of heavy gauge enameled solid core OCC high purity copper wire in twisted pair configuration. I thought to myself (Oh no, not this again). So the fellow lived near me and suggested that I take home a pair and try them for a week. Then, either buy the or return them.
O.K., why not!  After a week of some extensive listening and "fiddling", I was so impressed with most of the characteristics of what I was hearing that I handed him $50 and kept them. 
Well, wouldn't you know, over the past 7 years they ended up in storage also. - - - - - until two days ago !!
Very recently I have listened and investigated MORROW cables. A friend bought a pair of phono cables and was amazed. M-M-M-M This is one I passed up. Should I give them a try? O.K. , so I did. The one drawback being that MORROW claimes that some sort of "MAGIC" is supposed to happen after 400 - 600 hours of breakin. Of course they could speed that up with a burn in cycle for a considerable price. I didn't pop for that.
Been using them for a couple of months now, with some mixed results. There were days when they sounded odd; - - almost muddy, but then cleared up. "What's going on here" MORROW said that would happen.
Anyhow to get off the subject of MORROW, - - - - - - -
Three or four days ago, I decided to start cleaning out my collection of audio artifacts. In doing so, I ran across the old RED "ALLIGATOR" cables, as I fondly called them. You know, - - - - I never actually tried them. Well one of my current setups is pretty much modular with components in a open rack. Plenty of room to fool around. So, I disconnected my MORROW'S and plugged in the "RED ALLIGATORS".
Didn't have to concern myself with them lying on carpeting because they are more than stiff enought to suspend themselves. Subsequently, I discovered my RED interconnects, also solid core. You know, I never tried using all solid core through the entire signal path.
To end this long pile of sh _ _ ! After warming up the system for about 1/2 hour, I though I'll try a little serious listening. After about 3 minutes of listening to a VERY familiar CD, I stopped ! I have to try another CD that has always sounded a little harsh, being too closely mic'd. 
All I have to conclude with, is the results were astonishing to say the least. Without any rservation, I was hearing the best overall sound I have ever heard out of my system. ROBUST; VERY DYNAMIC; while at the same time, sounding PURE and TRANSPARENT without any noticible harshness in music passages that had always been there with virtually every combination of wires I have ever tried. Dimensionality of voices and instruments were well placed with appropriate emphasis, in a 3D soundstage, more so that ever heard previously.
You can call what I have said here, a pile of "bull".  Also keep in mind that what I have done here would not be very acctepable to most audiophiles for any number of reasons, but - - - -  If anyone out there is curious enough to locate similar cables and try what I discovered, I believe that you to will be astonished at the totally beautiful sonic presentation. THAT'S IT !!