Got the same set and also like it a lot, I think it's very good value for money soundwise. Sometimes I could use a tad more warmth for the female vocals but otherwise great sound quality.

My Stax SR-507 really "sings" when listening to:   Allison Krauss - A Hundred Miles or More - Jacob's Dream Allison Krauss - A Hundred Miles or More - Down To The River To Pray Allison Krauss - A Hundred Miles or More - Whiskey Lullaby Anne Akiko Meyers - The Four Seasons - Concerto No. 4...

Would say it's significant enough to notice - more on some tracks than others of course. A bit less bass, a bit less monitor-like and more airy. Soundwise it will put you closer to the ER4S sound than without imho.

I picked up an 75 ohm adapter from fleabay like this one (not from that seller, just an example) when I bought my HF3 http://www.ebay.com/itm/Etymotic-ER4P-to-ER4S-3-5MM-plug-resistor-adaptor-/271363212964?pt=US_MP3_Player_Cables_Adapters&hash=item3f2e8206a4

Having only listened to my brothers RE-400 very shortly quite a while back I can't say much about them besides that my impression was positive.   I do however own the HF3 which basically is a HF5 with inline mic/remote and can say that they are excellent at noise isolation with the triflange...

AKG K3003i ≈ Heir Tzar 350 > Ety ER4 > Heir 4Ai > Ety HF3 > Klipsch S4   Have or had all

Listening to music just now with the chain Macbook Air > MF VLink II > Heed Obelisk DA > O2 > Heir Tzar 350. Sounds surprisingly well....actually awesome at 1x gain and with 15V psu.      

Am about to get an O2 and have the possibility to choose which two gain settings to get. Still don't find it being clear to me which will be optimal after reading the numerous posts in here. Thinking 1x gain for the first but dunno what second setting to get.   Use case will be either...

set to high

Tri flange usually gives me the best result. They go deep and cancels out any issues with different sound due to "optimal" placement in ear.

Quote: My 2Stepdance is dead silent until around 2 o'clock on the the volume with the iems I have tried which varies from Etymotic HF2 (low impedance), Etymotic ER4PT with 75ohm adapter (100 ohm) to Heir Tzar 350 (350 ohm). That said I never get that high on the volume so it's a non issue...

Regina Spektor, What We Saw From The Cheap Seats has some very good tracks Lady Gaga, Poker Face, Live at The Cherrytree House Session 

Had a short listen to an Argon HA2 a year ago or so and wasn't that impressed with the sound but we all perceive sound differently  Happy to hear that you found something you like the sound of - I do however think that you will find that the HD650 will scale well beyond the HA2 should you...

Quote:   Excellent value for money imo - annoying microphonics but good sound and the highs are just straight out amazing with female vocals.