Yeah the conversion is extremely simple. I like 300DIN for everything too.
Since your wife already has DS4's, you might want to get two more DS4's for interchangability and standardization. On the other hand, the TX100's are quite nice for doubles too -- slightly better hose routing. Unfortunately, the current TX100's have that 1/2" port, but that's not an issue if you're using argon -- only if using backgas for suit inflation.
It appears as though the new Zeagle Flathead has changed it's first stage to having all 3/8" ports. I've been doing some research and talking over the past few days, and Apeks is now considering discontinuing the 1/2" ports on their regs. This would be great, but who knows when it would happen.
As it stands know, I prefer the DS4's for their standard ports, extreme reliability, superb performance, and lower cost. Maybe someday I'll pick up a couple TX100's if they get rid of the 1/2" ports.
Good luck.
Mike
Anyone interested in having Apeks change their regs over to standard 3/8" ports should shoot them an e-mail to help persuade them
.