Preamp to Pair with NAD M23

@erik_squires makes an excellent point.  There are some neutral tube preamps that may be a big improvement in several ways over what you have now.  I’d recommend taking a look at the Linear Tube Audio MZ2.  I actually bought this to replace my beloved BP6 if that tells you anything although I unfortunately haven’t gotten to listen to it yet.  Here’s a nice used one at a 42% discount from its current price and comes with the all-important linear power supply upgrade, and if it doesn’t blow you away you can just turn around and sell it for little/no loss — well worth the risk IMHO.  The tubes in this thing last a looooong time and are cheap to replace, so don’t let that dissuade you, and as a bonus it’s a first-rate headphone amp if you ever swing that way.

https://www.usaudiomart.com/details/650017308-linear-tube-audio-micro-zotl-mz-2/

I tend to be a tube fan, especially in a preamp.  In addition to the potential for stellar clarity, you can roll tubes to tailor the sound to your liking,

Thanks everyone for the suggestions.  I went with the Linear Tube MZ2 after checking out some reviews.  I'll report back on the sound when it gets here.  

Congrats!  You made a great choice and am sure you’re gonna be thrilled.  If you don’t already have headphones you might look forward to getting some in the future because it’s one helluva headphone amp as well.  You can get excellent sounding ‘phones in the $100-$300 range these days.  Let us know what you think once the MZ2 settles in if you could.  Did you get the LPS?