Need help with whirlpool tub rough-in!

I need to install a Hansgrohe whirlpool rough-in (valves, faucet, handshower) in a pretty tight whirlpool tub enclosure (tighter than I expected!). The rough-in comes with short 1/4" type "K" copper tubing (3/8" OD) which puts the individual components on 5" centers using compression fittings. I've only got one location for which this will work and accessibility after I drop in the tub will be nil. I'd like to separate the valves from the faucet (with diverter) and handshower, but I don't know how best to do the connection over what will be a 4-5' run. Certainly, I don't want to run 3/8" OD flexible copper as I'd be concerned about diminished flow - I need to get 60 gallons into this tub. I can run 1/2" copper pipe, but what then is the best way to terminate the copper pipe and then connect to the rough-in?

After looking over the options it seems like a 3/8" to 1/2" compression coupling should do the trick, but is there anyway to avoid the stub of 3/8" OD pipe between the valve and the compression union? If I have to go this route I'll make sure to support the 1/2" OD soft copper very near valve.

I can plumb around this tomorrow, but I've got to get this figured out soon!

Rick

This is when using pex is so helpfull.

It's flexible, and won't kink like soft copper.
I wouldn't run less than 1/2" for a tub like that.

If i use pex instead of the 1/2" copper I think i will still need a pex-to-3/8" compression coupling unless there is a way to connect the pex directly to the 3/4" fitting on valve and faucet side. Am open to suggestions!

I did check with Hansgrohe and they said the short stub of the type K would support 12 gpm.

faucet

12 gpm but at what velocity? I have never seen a Roman tub faucet with less than 1/2" stubs on it, (in fact 3/4" is more the norm), but maybe Hansgrohe decided to save money by going undersized.

I haven't calculated the velocity, but it's going to be very high in a 1/4" ID pipe. That's life, I guess. Hopefully, things don't wear out too fast. I've looked at other Hansgrohe rough-ins and the fittings are definitely larger. I won't actually be drawing 12 gpm in any event, but I don't want to add to the problem when I remote the faucet.

Pex or similar would be better between than 1/2" between valve and faucet since I would like to keep the short stub of 3/8" OD on each end (necessary because of the size of compression fitting) to an absolute minimum length. If I use rigid copper between the valve and faucet locations I'll need several inches of the 3/8" in order to have enough "play" to insert the soft copper into the compression fittings. Does anyone make a coupling that transitions 1/2" (or larger) pex to a 3/8" compression fitting?