I don't think SH4 utilizes the additional capabilities of DX10. The water in 1.5 is slightly improved over 1.4. I'm satisfied with it, especially with some mods like Operation Monsoon and Spax's German speech fix. If you get the UBM add-on, you will first need to deactivate the mods with JSGME if you have it. If you don't, first reinstall the game the install the add-on. I don't think the add-on will even install if you have a modded SH4 folder. Once you have it installed it's time to start modding it with 1.5 compatible mods. Definitely download the ones I mentioned above. They greatly improve the German side of things!
If you get the add-on, I'll make it easy for ya...
Here is the link for Operation Monsoon.
http://www.subsim.com/radioroom/showthread.php?t=134922
Here is a link to that German sound fix.
http://www.subsim.com/radioroom/show...7&postcount=87
One other thing, if you use Trigger Maru Overhauled, you will also need the TMO Enable U-boat ver3 mod. It can be found on the main TMO forum page here.
http://www.subsim.com/radioroom/showthread.php?t=132330