I have had my Spark since the end of November. I absolutely love this amp. I have a heavily modded Doge 6210 tube amp, Millet Max, and a custom DIY 7n7 transformer coupled tube amp lying around here and I definitely like the Spark the best. What people say about the punchy bass, superb mids and the smooth treble .... and the overall coherency are spot on. I was going to buy the Massdrop DV 336 SE but I cancelled because I did not think the DV plus the 6xx will better the Spark with the M1060/58x. I have had that combo before and I do not remember them being anywhere near as enjoyable. So, I bought a second Spark for work.
I tried the MP M1060 headphones and the Sennheiser HD58x, Senn 6XX and my assorted Alessandro headphones with the above amps and kept rotating. I always enjoyed the Spark the most. I also absolutely love the M1060's and the Spark plays like it was made for them. The Senn 58x are also extremely A+ good with the Spark. My Alessandro's sound as good as always on the Spark.... which is great.
I have been away from headphones for several years and I could not believe all the new companies and choices. But, actually my end game seems settled already. Buy a Spark and a M1060 plus a Senn 58x and just listen to music. I think about the Massdrop CHT and the CLC amps but I find the music so very satisfying, as is, why bother? I know of no other headphone that IMO, can beat the M1060 without spending a fortune. Ditto for the Liquid Spark.