I use my F1500 on transverter and RX ports with a 1mW to 25W HF amp from an old commercial radio that splits the inputs. The 1500 needs outboard filters on TX and RX and so does the amplifier.
The antenna is an inverted L for 160M with a 600uH variometer and 2:1 autotransformer. 50ohm to 25ohm.
The 6500 is much cleaner on TX and RX. I am working on matching it to an HF amp for 200+ W.
The Signature series radios are great on RX for 2200 and 630M with the Pixel loop.
I am using my F6500 for RX and TX on both bands with good results. A small broadband amplifier at the transverter output (50mW) driving two separate power amplifiers one for each band. The power amplifiers are modified ex DECCA system FET PA’s designed for 1kW out. My best DX using WSPR on 630m is 9511 km (PA to FR5ZX)This is IMO the best way to go, RX needs no additional filtering unless you live next to a medium wave transmitter and for TX you only have to amplify the 10mW of the transverter output to a suitable level. Additional mixers and oscillators can only decrease the performance.