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

Looking at the schematic, I'm not sure it's not buffered by the gain stage to a degree. The entire length of the resistor ladder is fed by the MOSFET with the direct source line tapping into the ladder at RV6. It looks like the ladder just attenuates the MOSFET gain below the line level further down the ladder. 

If your talking about the Aleph L there are two versions. This mkII passive patent pending one as he puts it:
"The only component in the signal path is wire and switch contacts."
Then it becomes active when the volume goes beyond 3 o’clock.

Cheers George

I looked at the most recent service manual from Pass. It's got both revisions. The original has no such direct connection. The revised design really only attenuates the gain below the line level. The gain stage isn't on its own discreet ladder. 

In my experience, I thought I was looking for a magical mystical linestage that money could deliver, but I was actually trying to correct abnormalies in the speakers.  When the speaker were great, direct from DAC was glorious...but still open-minded.

It is a provisional patent, which has maybe been granted by now on this special circuit, he may not have given the secrete to how he bypasses the "active stage" in the the schematic so it runs totally passive, after all it is patented. I've seen other manufactures post schematics and leave out their special circuits. Why no Nelson.

His words

 "The only component in the signal path is wire and switch contacts."

This means nothing active in the signal path.
Same goes for my Lightspeed Attenuator there is nothing active or any switch contacts in the signal path just a passive ldr, yet it is powered by the mains for the leds to function. Yet it is a passive preamp with no gain.

Cheers George