Koetsu black, lacking bass

That doesn’t sound right for a Koetsu, even fresh out of the box. I personally didn’t have stellar results with the Clearaudio pivoted arms and Koetsu (Jade on a Universal 12” arm), but I’d still suspect something else going on, like the phono stage and its loading (besides the usual suspects of alignment, VTA, VTF, etc). What is your loading? Koetsu tends to like 50-100 ohms into active MC stages, or a SUT with 20x - 30x ratio into a typical 47K MM input. Also, I’ve experienced bass lightness when using an MC stage with too little gain (60 dB or less for the Platinum models @ 0.3mV output). You might try a SUT like the Bob’s Devices Sky 20 or 1131, with your phono in MM mode, which will solve your gain and loading issues, and will certainly get near the very best bass impact a Koetsu is capable of.

His Magnify arm is a hybrid magnetic bearing (not as bad as the fully magnetic Clarify, but still), so I’d be wary of adding mass to that system (e.g. the tail wags the dog). Koetsu seems to like high mass AND rigid bearings, AND I haven’t had good results with Koetsu stone on the Clearaudio carbon fiber wand, so the tonearm is definitely in question as a possible culprit here.