unfortunately it is not possible to use VO DLLs directly with X#. Currently X# supports VO code only through the use of the Vulcan runtime, until the development team releases their own runtime.
VO 2.6 is very old, and newer VO versions have a much stronger compiler to prepare the code for the .NET migration, so you will have to make adjustments in your code.
But IMHO you should take the time now and learn to use X# with the .NET framework, maybe for new applications. Then, when the runtime is ready, you are prepared for the migration.
X# and the .NET framework give you a lot of new and very interesting features, new language constructs and GUI enhancements that are not possible with VO and its over 20 years old GUI classes - so it is important to learn .NET with the Xbase language you know.
It may not be helpful, but you should absolutely spend time on learning how to construct applications now with all the possibilities that the .NET framework offers.
for the RDD you have to wait a few months, I think - if you are not willing to buy a Vulcan license for the meantime.
In the last year the development group has worked very hard to finish the compiler (and it works very well!), but as Robert has announced here, shortly they will beginn with the development of the runtime libraries and the RDDs.
But nevertheless you should begin now to work with X# to see what WinForms or WPF offer. It took me over a year to understand where I want to go, first with Vulcan and now with X#.