It seems that if you're willing to spend around ~$700-900, the MAD Ear+ gets the vote almost every time. But what about less than $500, and preferably less than $400? What amp, preferably tube-based, synergizes well with the Grado RS1 headphones? --- On a sidenote, I'm finally getting around to upgrading my iBasso D1 / SR225 combination, which has been absolutely amazing. The setup really came together after hiflight's recommendation of the LT6234 / AD746 / LMH6643 opamp combination. Very smooth, warm, tube-like sound and improves the soundstage of the SR225s considerably. I also have an iBasso D10 with the topkit, and I'm actually not as impressed with it as much as I am the D1. It just doesn't have the musicality that the D1/SR225 combo has. I threw my friend's RS1s in the mix, trying to decide between the D1 and the D10, and it became even more confusing. The RS1s are definitely better, but I think I almost preferred the D1/SR225 combination more than the D1/RS1 combo, and maybe even the D10/RS1 combo. Just more musical. The opamps in the D1 throw a wide soundstage that really helps the SR225s, but becomes TOO wide with the RS1s. The D10/RS1 combo was better in most cases. I was only able to listen casually for 20-30 minutes, and I didn't take notes so this is just off the top of my head two weeks later. --- I've come across the HiFiMan EF2, Millett Hybrid, Little Dot I+, and maybe a few others that I can't think of right now. But what synergizes well with the RS1s? Bonus if it has a DAC, but I'll probably use the D10 as a DAC otherwise.