How much do I need to spend to get a preamp that sounds better than no preamp?

balanced lines offer less coloration even if they are only 6" long

6" This is false, your either hearing things or your biased toward your own retail preamp product.

In many cd players or dacs I've seen the balanced output is just an added opamp changing the "real' single ended circuit to balanced. Same goes with the input of many poweramps, which btw are single ended output to the  speakers. 
The only time balanced is better from source to to pre, or pre to power is for noise cancellation with interconnect over 5mts>

Cheers George  

tweak1
It could be that my system is 100% balanced, Isn’t everybody doing that by now?

Here is Nelson Pass’s take on balanced vs single ended.
When asked by an owner what sounds better on his X350.5
On diyaudio.com

Nelson Pass The one and only Join Date: Mar 2001
"Except for noise, it gives pretty much the same performance, and this is
because the inputs are summing junctions, and single-ended inputs are merely another balanced source with ground as the (-) input."

Cheers George

george, you just proved Ralph's point with help from Nelson. Noise is audible. The rest of your post is BS pushing your product.

When I first switched over to XLR, decade+ ago, I compared a 0.5m v 1.0m of the identical run of the identical XLR ICs. The difference was immediately apparent