i was using the algorhythm solo with the mk2, and they have excellent synergy. the original SOLO is the best IMO, the newer ones like the -db have a balanced imput and output, but unless you are going to go with the mk3 - +B Amp with a in and out balance that you can fully use balanced in and out, i dont know that its 100% worth it.
the newer cypher labs CLAS have the AKM Chip's vs the original has a referance series wolfson.
i feel the wolfson solo has better bass than the akm chip seems a little more thin.
i Sold my SOLO and went to the Ibasso db2 so i could use the iriver ihp-140 with fiber optic output. IMO the db2 has excellent bass its much like the CLAS but obviously they are simular and different as they both use the wolfson dac chip so they are going to sound simular and different as the same time.
in my expierence, with the hpp1 it too is using the akm chip and it feels a little sterile and cold, IMO thats the AKM chip it sounds a stitch thin and calculated.
where as the wolfson dac chip is warmer, it has better bass, and give you a sense of space to everything.
once i went with a DAC i never went back to no DAC, i dont care what amp im using, im going to be using that amp with a dac, the dac just seems to add so much more to the whole equation. if you go to a dac, you will see that.