Looking for $20k system for Mahler No 6

you should try the clayton amps. They are awesome and will give you the sound that everyone loves from tubes and the reliability of solid state.

My blatantly biased suggestion...

Speakers - Dynaudio C4's ($9K used)
Amp - Plinius SA 102 ($2.8K used)
Pre - Aesthetix Calypso... w/good NOS tubes ($3.3K used)
Digital - choose from Audio Aero, Esoteric, Accuphase, Ayre ($4K used)
Room Treatments from GIK Acoustics ($1K new)

I have no affiliation with any of these companies... just a happy customer.

The C4's really are great with large scale orchestral. Your room should be large enough to accomodate them, but I strongly recommend adding room treatments (bass traps & panels), as I recently found out they make a huge difference for very little money.

Well when you check out my system you will see I am highly biased when I pick the following components. But I listen to lots of classical and it sounds nice on my system, and I would think this would do it for you. All these but the Krell are in the used forums now, that Krell amp comes up fairly often.
Esoteric X-03SE 4100.00
Ayre K-1XE 4400.00 OBO
Krell FPB 600 (around $5.5K used)
Thiel CS7.2 5500.00 OBO
Anyway we all know what opinions are like, and this is mine. I would find every shop within reason of where you live and start auditioning everything you can. Have fun.

I would start with room treatments first. Otherwise, you are simply trying to fight the laws of Physics (or acoustics, more accurately). Room modes, peaks, etc. will significantly degrade the performance of even the greatest components.

Have Rives Audio do a room analysis and design. Then, the sound from $5k system will be more accurate than a $20k system in an untreated room.

A Different Approach For Your Consideration:

QSonix Server (Audiogon Demo) $3400
Salk Sound HT3 w/Deqx room correction & 3 way digital X-over $8500
2 units Wyred 3 channel x125 watt ice power amp $4000

Total $15,900

You have some change left over for finish upgrades on the HT3 or dinner out.

I haven't heard this system, but anyone starting from scratch with your budget should probably (at a minimum) investigate the Deqx/Tact/Lyngdorf approach. The speakers and amps liisted here are illustrative of this approach - you may prefer other examples of the species which fit your budget.

OTOH I have heard the QSonix which has a knock out user interface - Mahler and every other CD you own easily accessible via touch screen from a hard drive which, in many camps, is the prefered transport. It certainly sounded very good on demo at my local dealer. Enough so that I am awaiting delivery of my new QSonix server.

Good Luck

Marty.