Conrad Johnson Art vs. Premier 16 LS II

I have a friend who has maxed out his system pretty good. He has been running a premier 16 ls ii with unbeleivable success.

He is now at the point of chasing phantom upgrades and I was thinking of recommending an upgrade to a art as its about 2x his upgrade budget but i think it would be a much bigger than a 2k power cable to his ac conditioner, all cables except that one are top flight, that is a decent cable.

What could one expect to see in the upgrade of a premier 16 LS II to a ART or ART II?
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I would think the preamp change would do more than a cable change.

I have an ART II and III. For me, they are the perfect preamp(s). Haven't heard the 16 so I can't tell you what or how much of an improvement the ART is but I'm sure the "diminishing return" rule would be in effect.

What amp/speaker combo does he run? Usually that's where the best bang for the buck comes from.
I owned the CJ 16 and liked it a lot. However the TRL Dude tube preamp was a utter and complete revelation to my music compared to the well respected 16. Based on this experience please do yourself a big favor and consider the Dude.
I had both side by side. 16LSII is great. ART2 is beyond great. What they said is true that 16LS is 90-95% of ART. For financial reason, I had to sell both. I am looking to buy one of them back.