After a lot of digging around I found the firmware I was looking for. It appears that my NVR-7090 is the equivalent to the DS-7608NI -E2 from Hikvision.
I flashed NVR_K41_BL_ML_STD_V3.4.101_181024 firmware from the Hikvision UK firmware portal without issue and everything is working fine so far.
My cameras are the Swann SRNHD-836CAM model. Found the equivalent Hikvsion to be the DS-2CD2342WD-I. I flashed the IPC_R0_EN_STD_5.4.41_170312 firmware to the units and everything is working great!. I should note they did work with the PVR prior to flashing the Hikvision firmware. They did lag a bit with liveview so I updated the cams so everything is Hikvision.
I can connect to the PVR with the Hik-Connect app with is much better than the Swann app. Also the iVMS-4200 app connects to the PVR without issue. The web version direct to the PVR works amazing as well. I can have all the cams on stream 1 without lag. The Swann web version struggled with this at the best of times. I always had to select the sub stream.
Also the Hik-connect app is so far ahead of the Swann version its not funny. The picture quality is way better also digital zoom is great!