Unfortunately, many of the potential options are out of stock. If you are in a hurry, you may have to settle for one generation older tech. However, if you are thinking Powerbox, I would recommend a Mercury. It has the Gyro built in and has multiple battery and Rxer inputs. I have several in jets and giants. Smoothflite also has nice setups too, if you can get one. Look around, there are several options.
I have tried and researched several different setups and have settled exclusively on Powerbox Mercury SRS, for now. I have at least 5 PBoxes in the fleet. In my experience, nothing beats a PBox Mercury SRS with at least 3 remote Spektrum SRXL Rxers. I have been using PBox for several years.
However, you are using Futaba. I am NOT familiar what you would use in a PBox for the multiple Rxers with Futaba. Larger models not only need multiple power sources, but also need multiple Rxers. Some power distribution systems offered may not be capable of handling several Futaba Rxers. Some models only allow one Rxer.
There are also some battery combining devices out there that do NOT involve multiple Rxers, etc. However, they just combine two batteries and do not regulate the voltage. Regulating voltage is important for larger aircraft and when you are using Low Voltage servos, etc. Today's larger planes need LiPo batteries, High Voltage servos and multiple receivers as well as lots of battery power. The chain is only as strong as the weakest link.
Look closely at what you are buying before you pull the trigger. Make sure you are getting what you need or may need in the future. Hopefully you can get your hands on what you want in a timely manner.