I now have a Rx in my possession and have been comparing it with the iQube (v1) last couple of days. My Rx has about 150 hours or so on it so fully burnt in. Headphones are Senn HD25, my source is a Pico DAC and cables are all Jena DIY. So here are my initial impressions.
The the Rx is a very nice amp, cosmetically and sonically. I was also surprised how close the Rx and iQube sound, so my brief notes below are not night and day differences but certainly there.
I thought both amps had good and almost equal soundstage. Nicely open and spacious. The iQube is known for its neutrality and I was surprised by how neutral the Rx was. I didn't really hear a house sound, which is a good thing. Wide open window to music on both amps. Great job here as there aren't too many portable amps in the same league as the iQube with regards to neutrality.
While the Rx has a crisp and clean treble reproduction it lacked the extension the iQube has. I also felt the Rx's treble at times sounded slightly metallic in comparison. iQube wins in this area.
Midrange was about the same. Both have a very transparent midrange reproduction. I couldn't really pick one over the other.
Bass was interesting. While the Rx has more bass presence than the iQube, the iQube had deeper bass extension. While you may initially feel the Rx has "better" bass, its because its more emphasized. I cant pick a winner in this area. On some music, I appreciated the added bass emphasis the Rx gave me but in certain cases I preferred the iQube.
So in summary, I still prefer the iQube over the Rx in my setup.
P.S: I purchased the Rx from another head-fier for this review and my job's done, so if anyone wants to purchase a like new Rx, PM me.