The HH referring to pickup configuration HH is 2 humbucker similar to jazz set but with 2 H.
As for the sub4 and Ray4 it’s just the different model year. Sub4 is older than Ray4 which older than sterling Ray4 sub series.
MusicMan company has a department of dedicated staffs to find the way come up with names that would not only confusing to consumer but intertwining with there other models.
Their models
stingray bass
Ernie Ball Sterling, named after his son, the high end one with smaller body and head stock. Fantastic 3 mode pickup and electronics features Jazz neck nut width.
Cutlass bass, their version of a P bass, fantastic bass. However there’s another earlier cutlass bass that looked just like the stingray with graphite neck back in the 80’s the new one is not a redesign of that bass, they just ran out of name. It’s also the same name as their popular electric guitar line.
The Caprice is the PJ version of the cutlass.
Then you have the reflex bass, also advertised separately as the”game changer bass” it uses the Axis guitar body platform with crazy pickups options and I kid you not on board computer so you can upload and download your setting.
The next one is the BMW designed Bongo bass, it’s one of the most comfortable 2 octaves bass I’ve played to date.
The most confusing model name has to be the SUB.
Let start with the best
Ernie ball MusicMan SUB, made in USA. Fantastic bass slab body excellent industrial painting finish very rugged stingray. Black head stock.
Sterling by MusicMan S.U.B.
Sub4
Ray4 sub series all are the same bass.
Their Ray34/35 series also have a little confusion
The Ray 34Ca is not made in San Luis Obispo, California. The CA stands for classic active. They assumed that everyone know that the classic preamp is with 2 band EQ in stead of 3 band “modern” EQ.
Except for the game changer I own all of these basses in various pickups configuration except for the HH. They are very confusing then trying to put it on the market.