Do you mean the TUSA RS 460?
The R400 first stage is identical to the Scubapro Mk 16. (Scubapro contracts with Tabata to have them manufactuer Scubapro designs, and TUSA = Tabata USA.)
The S60 second stage is identical to the R380 and as such performs identically to the nearly identical R295.
So in effect your reg will perform identically to a Scubapro Mk 11 R295 or Scubapro Mk 17 R295, so neither of those would be an "upgrade" unless you need a sealed reg for cold water and in that case the Mk 17 is a good choice.
In terms of getting more advanced, your first stage is fine (unless you need a sealed first stage for cold water diving) and while there are some first stages that will deliver more gas, it is overkill as the R400/Mk 16 delivers more than enough gas even for deep technical diving.
Your recond stage is where improvement can be made by going to a balanced second stage. And if you are going to get a balanced second stage, you just as well get one that is adjustable as well. I like the Scubapro G250V as it is a high end second stage that delivers plenty of gas and can deliver excellent inhalation an work of breathing scores. It, along with the original G250 (as opposed to the G250HP that came in betwen them), is a mainstay of deep technical divers.
It would also be a great match to your TUSA R400 first stage and could be serviced by any Scubapro dealer - provided they acknowledge it is truly a Mk 16. Some may get funny over the liability of servicing a reg they are not a dealer for and others may just try to sell you a Scubapro first stage as well as the second stage.
Personally, I use Mk 17 G250Vs for both backmount and sidemount cave diving.