Pre-amplifier suggestions

Back in July, I asked for SS amp recommendations.  Since then I have acquired some Krell "KAS" monoblocks and some ML 33H.  I have listened to both fed by an ARC Ref 3.  The Krell were more revealing, the ML sounded dark.  This difference prompted me to dig out my Pass Aleph P (pre).  With the Aleph there is an immediate and extremely noticeable improvement across the entire range.  Now, i am wanting to upgrade my preamplification. 

I am considering the following preamps in no particular order:
1. Dartzeel
2.  Esoteric Grandioso C1
3.  Vitus
4.  Solution 520
5.  Boulder 1010
6.  ML 32 or 52
7.  Nagra Classic or HD
8.  ARC Ref 6
9.  Absolare Passion
10.  First sound
11.  Atma MP1
12. Bat Rex

As you can see I'm all over the place...The Krell KAS has balanced inputs,  the ML has both balanced and single-ended inputs.  I use long balanced interconnects, the amps are 16 ft. away.  If you have experience with either of these two amps, please provide a preamp suggestion.  Lastly, I would like to keep this under $15K (preowned).

Best,
Jose