Sounds like your cousin is an accomplished piano player.  I know that Bachus has been talking about 88 key arrangers, but how about vArranger2?  If your cousin is so used to the piano hammer action, he wouldn't want a 61 or even 76 key arranger.   I have been looking for a compact 88 key board.  I looked at the Roland A-88 controller, but it is a bit expensive, and as a midi controller no built in sounds  or speakers. Built-in sounds in case of the notebook freezing on you.   The new Numa Compact 2 by Fatar is indeed compact with a number of nice features and sounds at $499, but semi-weight.   By the way, I had purchased a PX5s for a church group overseas.  That is a very nice keyboard.   As I was preparing the keyboard, I found out that there is a huge group of followers and a wealth of info for the PX5s.  The PX5x got me interested in the PX560, but I already have am 88 Casio board.  So I am leaning towards the Numa Comapact 2.   I did try it out at NAMM, but spent very little time on it at the time.
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"You Shall Know the Truth, and the Truth will set you free." John 8:32