did anyone point out that your mackie most likely actually does have more outs than 2? Does it have inserts? Even if it doesn't, you aren't "tied" to using the "tape outs". All you need is some rca-to-1/4" cables to start using the inserts, main outs, mons, and/or auxiliaries, all on separate channels.
Falken has a good point here. I do believe most Mackie mixers has inserts. This way you could hook a insert cable up (stereo jack to 2xRCA) and tap the signal after the preamp and EQ-section. THe beauty is when you hook the outout from your recorder on to the same cable, and gets the signal back into the mixer channel.
The signal chains then becomes something like this:
Mic -> Mixer Preamp -> Mixer EQ -> Insert OUT -> Taperecorder IN ->Tape -> Recorder OUT -> Insert IN -> Channel fader -> Master Mix
Many Mackies also has 4 Aux sends or several Group Outs, wich all can be used to tap the signal into tape. The beauty of the above mentioned method is that the Mixer Strip is not rendered useless after just tapping the signal from the insert., as it goes back into the fader and turns into your monitor mix
I wouldnt recommend buying a "new" mixer if your Mackie has Inserts for every track. Although you soundwise might benefit from it. And that is beyond my experiences, as Ive never seen or heard a Tascam Mixer.