For the last 41 years, the Mark Levinson brand has produced reference-grade audio gear garnering praises from audiophiles the world over. For its 40th anniversary last year, the company (now part of the Harman Luxury Audio Group) pulled out all the stops to produce concepts for new top-of-the-line components. The No. 52 Stereo Preamplifier($30,000), which will begin shipping this month,is one of the shining results of that effort. In addition to its dual-monaural, two-chassis design—which keeps the audio circu…