After a quick browse........ The only difference between the two DXR and RX Digital,........ The DXR has an extra adjustment dial on the face of the alarm. So there are 2 dials that have an "S" on them (The bottom two).. These are both for sensitivity control... The first of these, 3rd one down, is for adjusting the sensitivity of the roller wheel and is governed by how much line you want to pass over the wheel before an indication is registered........ The second "S" dial, bottom one, is said to adjust vibration, ...... A micro adjustment, if you will.
The RX alarm has one single sensitivity adjustment dial. When you turn this dial all the way round to it's most sensitive, there is a "V" symbol on the dial reading, which stands for "vibration", in other words , it's mega sensitive..... IMO though Dan, I doubt you'd ever use an alarm set at its most sensitive as the slightest breeze or ripple even, will give you a lot of false bites.
Basically, the single sensitivity dial on the RX, does both jobs, that the two dials on the DXR do..
Side note... Those dinky little dials on the older alarms can be fiddly to adjust, especially if a little stiff. I use forceps, gently , if I need to adjust mine,. which isn't often.