Matthew,
I believe you said earlier, that bypassing with the .1 cap from 2 to 5 was too much and that you preferred it parallel from 4 to 5. Also, I did not mention this earlier, but the bypass info I have read said that roughly 10% is a safe max for not messing with phase too much. With a recommended 3 uf cap, and you using 3.3, you were already at 10%, but since going a little past 10% with the HR-1 was fine, I guessed another .1 would be OK for you too. And .1 does a lot for my sound, while .22, and .33 were good, but finally ended up being a little too much for me. But that was testing in my particular system and room.
And the ERR is a very different sort of speaker even than the HR-1, with the adjustable tweeter and radial driver, where most speakers have fixed front drivers. And since Zygi is not concerned about a higher value, going further with bigger bypasses could be quite interesting.
As I think about this, the questions would be: Since 2 to 5 is the same as 1 to 5, crossing with the .47 or .68, from 2-5, skipping the current cap and the resistors, would add highs and go deeper into the highs than the .1, but if I recall correctly, you found the .1 in this position overwhelmed what you wanted in the sense of low end balance. Alternately, if you increase the parallel crossover (4-5) by .47 or .68 it would go deeper into the mids, but the questions...would that be too bright for you after the .1 gave you a satisfying sound.
That said, what ZYGI said, the .1 cap only works up high, or in the case of your current arrangement, clarifying the high-highs along with being parallel, bringing the frequency range of your Mundorf down only a little bit to 3.4. So I am guessing Zygi's thought may be that by having a wider high frequency range in the blend than the .1 provides would be brighter on top, but also a wider frequency range of the highs, and this wider range may sound more balanced and better.
Did Zygi say what the frequency range of your tweeter is, or about what frequency the 3.4 cap crosses it at? If it is the tweeter I think it is
http://www.swanspeaker.com/products/products.aspx?cid=9&sid=52&pid=160 like my MG944 and HR-1, then the current version has a recommended crossover at 4500 Hz or above, presumably because of a deep frequency slope-off starting at about 4000, and down about 20dB by 2000.
If it would work without overload, using caps big enough to get down to 2K, trying to address your 2-3K dip area, may help a little even with this steep slope-off, especially if your current caps are already getting you down to 4K. But if your caps are going only to say 6K, a larger cap will crank the 4-6K range much more than the 2-3K range since the tweeter slopes so much below 4K. I think this is right anyway.
Looking for solutions....since your 10 ohm resistor is close to where you want it, an 8.2 ohm M-resist Supreme instead of 10 would be some risk, but you may really like this once you get used to it. The Mundorf is so smooth and solid sounding I remember that these resistors made a lesser value necessary in my system. The Wirewound 3 ohm was brighter feeling than the 2.7 ohm Mundorf. I am guessing the 8.2 Mundorf might bring your tweeter resolution up without sounding much (if any) brighter, but I can't say for sure.
If your room is canceling 2-3K in a notable way, this may be the primary problem in the sense of vibrancy. This is important midrange information for a sense of articulation and especially in the 3K range, there is information that implies presence.
This in mind, speaker placement could be interesting at this point of serious listening. Have you played with the speaker placement and/or tweeter angle lately? Even a little forward and back, and/or a little toe is discernable in my room. From very little up to a foot in any direction could really shift your room reflections...enhancements or cancelations. There may be a place where the balance sounds better to you.
Same with toe and/or tweeter angle.....
Another experiment might be: Since Zygi said up to 12 uf could be OK with the tweeter, if you don't have any other caps around, how about trying 6.6?...If you can set your system for mono...pull the speaker wires from the amp on one channel, and take the Mundorf from that speaker and put it in parallel on the other speaker making it a 6.6 value, and taking it much deeper into the mids. Not an ideal test as it would be only one speaker, but it may give you a sense of the possibilities.
Lastly, I have messed around with a number of favored, but relatively inexpensive caps, and if you want to try Zygi's suggestion of a .47 or .68, Obbligato Gold Premium and Mundorf Supreme were the realist, most natural sounding of the decent but relatively inexpensive caps I tried.