Had a chance to compare my Little Dot MkIII (Voskhod drive tubes) with a Graham Slee Solo SGR II with the upgraded PSU (on loan for a few weeks) feeding a Sennheiser HD650. My source is iTunes -> Audirvana Plus -> Audio-GD DI -> Rega DAC.
The LD MkIII perform really well compared to the much more expensive Solo. To make things more even, I set the gain of the LD MkIII to 10. My normal setting of 5 made the sound stage of the LD MkIII wider then the Solo, however at gain 10, the sound stage is similar to the Solo.
If anything, the Solo is slightly more coherent, better instrument separation and the bass slightly deeper then the MkIII. And to my surprise, the Solo seemed more laid back then the MkIII. On The Shin's Simple Song, it was more energetic on the MkIII then the Solo. The MkIII seemed to have slightly more snap to the top end. Both had similar levels of details to my ear. The MkIII is pretty resolving amp. I find both amps very musical, and would happily live with both. However, for the price, the MkIII is a real bargain in my opinion.
I'm glad I was able to do a home comparison of the MkIII to a more expensive and well reviewed amp in the Solo. The Solo is a nice amp, and nicely "analog" sounding for a solid state. But now I can be comfortable in spending on tube rolling on the MkIII. It is a good amp, and for the price, I dare say the best piece of audio gear I have ever bought.