I listened to the SZ2000 and the Z1R with a Micro iCan Special Edition, an iPhone 6+ and using an app called Equalizer and after elevating the sub-bass region, I would say with confidence that the Z1R has at least 90% of the bass that the SZ-2000 have. I hope I don't insult anybody by comparing these two headphones but I'm just talking here about pushing the sub-bass and bass. I'm still working on my audiophile vocabulary but even though the SZ2000 has more impact, the Z1R bass and sub-bass just sounded more engaging to me, and I just enjoyed more listening to the Z1R. When you go to the headphone thread for bassheads, the top 3 are the SZ2000, TH900 and the XB-1000. Well, in my opinion when you push the bass on the Z1Rs I would probably squeeze them between the SZ2000 and the TH900. Yes, I've heard the TH900 too and also used the same EQ app and the same AMP and to me, because they are semiclose, I feel that they didn't rumble as much as the Z1R, but that's just my opinion. Also the TH900 when I cranked up the volume, they got too hot on the treble and didn't like it. On the other hand the Z1R scales very very nicely with an amp and EQ, just like the Sony Z5 which is my favorite IEM right now. I also forgot to mention that I had the iCan Micro XBASS switch at the highest level and the gain switches also at max which is I think +24db. I hope this helps.