I'd try it another way. Connect the channel 7 yagi to the first LNA 200, then to the VHF input of a UVSJ but leave the UHF port empty. Combine the channel 8 yagi to the UHF antenna using a second UVSJ. Feed the output of the second UVSJ to the second LNA 200. Next combine the outputs of the First UVSJ and the second LNA 200 using a two way splitter. Finally, insert a 6 DB attenuator between the output of the 8/UHF LNA 200 and the input of the two way splitter.
With this setup your problem channel will be channel 8. There will be an optimum value of attenuation to balance 7&8 reception.
