OP, best not to go there if you have to ask here. If he's doin 150+ a wk, he prolly has his preferences. If you don;t know them, I wouldn;t try to guess, no matter what recs you get here. Hubby will surely be grateful and faun over your present, but the shorts will find their true level in his go-to wardrobe.
If you go for shorts, maybe do his favorite brand pr in another color. I.E., I ride navy shorts almost as much as the basic black.
I'd suggest something more 'utility' than shorts.
I.E., for me and many other riders, we go thru gloves on a frequent basis - I need at least 3 prs every yr, not counting full finger stuff for late fall thru early spring. 3 prs cost about the same as some medium price shorts...
Or maybe another pr of riding glasses...
a second helmet... always good to have another which is 'clean' and dry. I swap helmets often to allow me to wash them (they go into the shower with me) and dry for a day or so.
A second pair of shoes - and there it's easy, the same shoe as the other - shoes can be pricey
shorts are very personal, maybe the most of all the kit...

you said he doesn't have a favorite - but it would be good to know which he goes to most often.
and knowing his measured 'size', will have an impact on which brands might have the best chance of fitting. Again, some brands run quite small, some are very "american' sized, very few of the higher end will fit 'big'.
good luck