Use a file archiving program like WinRAR or 7-Zip to view the files in both packs.
Drag all of the folders and corresponding files under the assets folder of the Attack of the B-Team texture pack into the assets folder of the Sphax PureBDcraft resource pack, effectively merging the two packs.
Open up the Technic launcher, select Attack of the B-Team, and hit play.
Once the Minecraft client comes up, click on Options > Resource Packs > Open resource pack folder.
Place the newly patched Sphax PureBDcraft + Attack of the B-Team resource pack into that folder.
The new resource pack should be available now to select. If not, you may need to restart your client. After selecting, it may take a minute to load up.