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

No sir. And while I haven't read ALL the post on this long thread, everyone, even the arguments, are with the goal of transparency. the LEAST amount of change to the signal. 

If you are happy with no pre right now, that's great. General opinion here seems to think it's the best way to go. You could even take the money you saved and spend it on 5k of interconnect and REALLY have the most transparent set-up. 

There's lots of options.

I just closed a deal for a Hatton passive XLR, so will see whether it improves on no preamp. If no glitches, I should have it by friday

Tweak: sounds like a worthwhile experiment. 

Questions might be, is there a difference having the extra jacks and cables? Is the volume attenuation by the new per better than the digital of the Oppo? 

Is the Hatton buffered or is it just pure switching?

all good questions to be investigated

No buffer on this one, but they do make them

honashagen OP
If so just put a bunch of your favourite preamps in series and the sound would just keep getting better!

Yeah that would open the eye’s (ears), should just keep getting better and better until nirvana’s has been reached.
https://ih0.redbubble.net/image.121918664.8304/ap,550x550,12x12,1,transparent,t.u3.png

tweak1536 posts05-28-2018 5:04amI just closed a deal for a Hatton passive XLR, so will see whether it improves on no preamp. If no glitches, I should have it by friday

Can we know what your sources impedance and output voltage is and the power amps input impedance and sensitivity is, so there are no question raised?
As you’ve posted in other posts that you have a tube/capacitor coupled output Raysonic source, which would not be very low output impedance especially in the bass, for your experiment to be conclusive in it’s outcome.
Also do you have a link to this Hatton xlr pre, all I can find is stuff to do with bands/studio ect.  

Cheers George