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

Most everyone knows that the McCormack amps have high enough input gain that allow passive preamps to drive this amp and as a result sound spectacular.

I am familiar with your Audible illusions L1 preamp and I liked it a great deal. It was said to be the same linestage used in their more expensive model the Audible Illusions 3 which may be debatable however It may not be to your liking nor the ideal companion for your McCormack DNA-1. Several years ago when I owned a DNA-1 with a Revision A the best sounding tube preamp to my ears was the VTL 2.5, and everybody else in the household that had a high appreciation for great sound agreed.

+1 PHD.
As this tested McCormack shows, absolutely no need for an active preamp, when most sources are >2v or more out, and this McCormack only needs 828mV in for full output wattage. 

Stereophile: " Input impedance at 1kHz was a calculated 99.5k ohms, consistent with the manufacturer's specification of 100k ohms. The DNA-1's gain was very high, this gain ratio corresponds to a decibel gain of 32.4dB, implying an input sensitivity of 828mV for full 150w output."


Cheers George

I  did buy an axiom passive preamp. Although it is very good it lacks in bass and warmth for me.  I'm using the audible Illusions again.

Although it is very good it lacks in bass and warmth for me. I’m using the audible Illusions again.

That is the most common experience we hear about passives.

honashagen OP
I did buy an axiom passive preamp. Although it is very good it lacks in bass and warmth for me. I’m using the audible Illusions again.

The only reason for lack of bass, which would also rob warmth, is if the source’s output is "capacitor coupled", and that capacitor is too small.

It’s a simple fix to double the uF (microfarad) of the capacitor and at the same time use a better "quality" one, as most skimp here with average quality industry ones.
  
Myself, all my sources, and everything else is direct coupled, which has the best bass, and no "sound of a capacitor" in the signal path.

Cheers George