You should be able to find a little dongle adaptor that converts 9-pin to 25 pin D-subs. It's a completely passive connection converter that consts thruppence ha'penny and there should be dozens of them lurking around your local electronics junkshop. You'll just have to look to make sure it has the appropriate male/female sockets and if necessary find a so-called gender changer socket. Easier than soldering it yourself and figuring out the TX/RX/DTS/RTS connections. The same shop may well have a 9-to-25 pin cable which is less bulky and clumsy than the adapter.