Redirecting different front end ports to dynamic (srv lookup) backends (matrix-synapse

Help!
1

I need to add the 8448 port, I was thinking of adding this binding to the frontend https.
But how do I redirect the 8448 port traffic to the backend _httpsfed._synapse.matrix.dev._tcp.local (and keep 443 going to _https._synapse)

I have this configuration:

frontend https
  mode tcp
  bind 0.0.0.0:443
  use_backend _recir_synapse if { req.ssl_sni -i matrix.example.com }

backend _recir_synapse
  server loopback-for-tls abns@synapse send-proxy-v2

  
frontend synapse
  mode http
  bind abns@synapse accept-proxy ssl crt matrix.example.com.pem
  option forwardfor
  http-request return status 200 content-type 'application/json; charset=utf-8' string '{"m.server": "matrix.example.com:443"}' if { path /.well-known/matrix/server }
  http-request return status 200 content-type 'application/json; charset=utf-8' string '{"m.homeserver": {"base_url": "https://matrix.example.com"},"m.identity_server": {"base_url": "https://vector.im"}}' hdr Access-Control-Allow-Origin '*' if { path /.well-known/matrix/client }
  default_backend synapse
backend synapse
  mode http
  balance roundrobin
  option httpchk GET /_matrix/static/
  default-server check resolvers dnssvrs1 maxconn 200 weight 100 resolve-opts allow-dup-ip
  server-template synapse 3 _https._synapse.matrix.dev._tcp.local ssl