Magnepan 3.7i vocals sound harsh

I have recently been playing around with the resistors on my Magnepan 20.7s. (they have the same tweeter (interchangable) as the 3.7/3.7i).                   
Previously I have used no resistors on the tweeter or midrange.I did have a small handmade coil on the tweeter to cut ultra high frequencies, a choke tweek suggested in the past. Just Kimber wire around a dowel, 31 turns.                        
I started with the one ohm resistor upplied by Magnepan on midrange. Made the sound rather dark, heavy. I went to Madisound website (they sell speaker parts) and ordered a pile of Mundorf MOX 10 watt in 0.33    0.68    1.0    1.5    2.0 ohms .. The best so far has been to combine two 1.0 ohm to make 0.5 ohm resistance.  
So I recently ordered a couple of Duelund Cast (considered the best sounding speaker resistors in relevant reviews) plus many values are on sale nearly 50% off at PartsConnexion. I ordered pairs to make up a 0.5 ohm resistance. I plan to insert them behind the Magnepan connector plate, so I can further refine the resistance either by adding additional resistor(s) in the provided space, or just bypass them with the stock jumper. (problem with adding is can only go down in final value. But after using the 0.68 value, I feel pretty good about the 0.5 ohm as a baseline.)

John,

you our got some great hints here to help you.  I got your email and want to hear your system once you get this taken care of.  Once you get to the highest resolution that your system has, it’s the little things that can make or break it. 

Went naked no resistors which I think sounds best(probably some high frequency loss at my age).
Let the equipment warm for an hour much improvement in sound.
Tried 3 lp's Charlie Byrd direct to disc truly incredible, Basie Jam# excellent, Elton Madman some improvement. I also tried EJ on a friends system yesterday and could hear some of the same distortion but not as pronounced.
Maybe it the price you pay moving up the food chain the good sound better and not so good recordings worse.

OP, just finished reading all the above posts and you've gotten lots of good responses. One thing I remember reading about was a similar situation as yours, harsh vocals/good instruments on a particular recording. Turns out, the singers mic had been wired in reverse polarity, everything else in normal polarity. And because you have some of the most resolving speakers around (I own Vandies, but I do know how good Maggies sound), I believe that the resolution of your system is bringing up the good, the bad, and the ugly from your music collection. My experience is similar. In fact, I mentally grade each of my albums into classes A, B, C, D, and F based purely on sound quality.

Tom