Do I understand correctly that the stock bank of 4 LPFs in the uBITX are for
60m, 30m, 15m and 10m ?
The documentation says
3.5 to 5 Mhz
7 to 10 Mhz
14 to 21 Mhz
21 to 30 Mhz
Since these are LPFs then they have to pass the highest frequency in the range so 60m, 30m, 15m and 10m ?
The QRP Labs Ultimate Relay-switched LPF kit will handle 5 LPF filter boards so
it should handle these 4 band filters plus a bonus extra one for 160m.
The Raduino has three outputs TXA, TXB and TXC which are used to drive the relays for the current LPFs.
That works out to 3 bits which could be used to drive up to 8 unique relays using some sort of 3 to 8 line decoder/demux chip.
This would make replacing the LPFs & relays pretty easy and would require minimal Raduino code changes.