Software Audio Mixer for Audio Interfaces which have none?

Ites Folks,
I'm wrestling since a time with a very dumb problem. Let me explain:
I want to do audio broadcasting via the shoutcast winamp plugin. No problem if:

- you have a standard soundblaster compatible audio interface
- you just want to broadcast a playlist from Winamp

Problem if:

- you have a firewire or USB audio interface which has no Windows Software Mixer
- you want to broadcast music and use a microphone to talk a bit

Ok, at my place it is the following shituation: At my studio computer I have a Edirol FA666 Firewire Interface. It has no windows mixer. So when I try to configure anything different than "Use Winamp Output" in the Shoutcast plugin I get an error message telling me, that no mixer devices are available.
Same at Malinas PC: She has a Tascam US-122L USB Audio Interface which brings no Windows Mixer with it.

It's pretty logically, that these devices need no software mixer usually as they have builtin mixing capabilities and most people prefer to tweak physical knobs over using softwareknobs via the mouse.

But as I said, this causes problems, when you use software like Winamps Shoutcast which rely on a windows software mixer.

So my question is: Are there any generic software mixer applications somewhere out there which allow me to configure and use my audio device for Shoutcast.

See, it must be possible to do such a software, because for example FL Studio gives me full controll over all Ins and Outs of my Edirol Interface.

Thanx in advance

Sonny