Has anybody tried using single solid core cables?

Yes, I have experimented with solid core copper and solid core silver cables. The sound is unnatural, but it can make vocals sound better than they are.

I've come around to thinking it's all in the implementation and the particular system. Right now, I have solid core silver for my ICs and tinned, stranded copper for my SCs.
It's the best I've heard in my present system.

Coli, interesting personal observation on the unnatural sound and the betterment of the human voice. I know from recently using silver solid core SCs that voices were better presented than most other parameters of the musical event and that leading edges were hightened at the expense of the rest of the note. That could be why it was so engaging, at first, and then left me unsatisfied after.

I still believe that there are better made solid core SCs out there but they are beyond my financial reach.

All the best,
Nonoise

A good solid core cable can be competitive with a midrange stranded cable. But in the upper levels of performance, stranded cables rule. Some would say that the top level solid core Audioquest is competitive with the best Nordost, Cardas, MIT, Purist, but that's not my experience.

I recently after reading on the subject of Solid core wires I experimented with some 10Ga Solid core magnet wire in my system. I Have Infinity Irs Betas and I must say the results were quite good. This of course is a situation where this might sound good in my system but not so good in another system.

Yes, it's all system dependent. I went back to an older pair of solid core copper speaker cables and I now have the music literally in front of the speakers and all on the same plane. It's not quite holographic but the level of resolution is beyond what I thought possible.

The center fill is nothing short of astounding as everything seems quite palpable compared to before, with the images spreading out to almost outside the speakers. Couple it all with the resolution of a good pair of headphones and it leaves me scratching my balding head as to just why this combo of amp, cables and speakers sound so great and then it dawned on me that it wasn't until I got my speakers that it all came together. So yes, it's all system dependent.

All the best,
Nonoise