Mark Levinson Gear is not what is used to be! and Neither is Krell. Look at older pre-amps like CAT or even Tube Pre-amps from VAC their Reference design looks awesome! or ML-26 Pre-amp Dual Mono Design mid 80's from Mark Levenson.Or Krell KBL line Level used around $1000.
ML-26 would be a nice companion to your ML-23.