Need SoundCard Advice - PLEASE

Ok, so our setup may get laughed at, but it is what it is and there isn't enough $$ to start from scratch.  Oh yeah, throw on top of that we are learning as we go.  So with that said......
 
We have a normal Rock band, ie Guitar, Bass, Drums (electronic for 1st takes), 3 Vocal mics.  Sometimes it's 2 Acoustics, or 1 Acoustic and 1 Electric.  Anyway, we record to a Tascam 2488 Neo, which is great and gives us plenty of track space, 24 + Virtuals.  I know supposedly we could do the editing on that, but I'm more comfortable with software and being able to see the waveforms and such.  So tracks get laid down to the Tascam, then transferred to PC.  We are using Music Creator 4.  I think I'm starting to get the hang of it, and am comfortable with layering tracks, cutting/trimming, adding fx, compression, etc.  However, the final product does not sound like what we are hearing while mixing/editing.
 
This is where I would like you not to laugh at me outloud :).........
 
We are running the audio OUT from the onboard audio interface of the PC, to a Stereo system (a really nice system).  Are you finished laughing yet?  Anyway, I think the problem we are having is the crappy quality of the audio out.  When the tracks are played from the Tascam through the PA System, they sound good and that they need only some tweaking, ie EQ, maybe some Reverb on vocals, Compression, etc. But when played through the computer, they don't sound as good.  What is happening, I think, is I'm "tweaking" through Cakewalk, to get a good sound through the Stereo, via crappy audio OUT.  Then when I get it sounding pretty close to what I'm happy with, I dump those songs to a CD.  When played on another system, ie car stereo this time around they sound awful, EQ'd WAY off, levels not sounding how they did while mixing, etc.  So I think it has to do with inferior audio OUT.
 
I'm looking for recomendations on Sound Cards to help us out.  I do not need an interface to record directly to Cakewalk, we are using the Tascam to record "live".  I need a better representation of the audio OUT.  At least I "think" that's what I need.  $$ IS an issue, so I can't be buying a new hot-rodded DAW workstion.
 
Thanks!
 

I'll assume you're transferring the wave files from the TASCAM to MC track-by-track, and not a single stereo file.
Tweak each track, then re-record it into the TASCAM.

Yes, yes it is.

So, you're using an external CD burner, maybe the TASCAM?
Have you tried Windows Media Player to burn the CDs, or some other utility on your computer? Does that still not sound like what you hear coming from MC and the sound card?

Yes. CDs have to be 44.1/16-bit in order to play on most CD players. They won't recognize higher sampling rates and bit depths.
Strange that your burned CD doesn't sound like what you hear over the speakers. Just for fun, try recording the audio output from the sound card into the TASCAM and see if you get better results using the recorder to burn your CD.

Here is how i would handle it. First off i would record at 24 bit 44,100 sample rate in the tascam if possible the 24 bit will give good headroom, and the 44,100 will not require any changes or conversion.

1. record the tracks into the Tascam and when you are happy with them, export them on a CD as wave files and open these in MC. Make sure that they are all playing well and sound like they did in the  Tascam unit.

2. AS Beagle suggested in the mixer view in MC add a stereo buss and name it master, and have that output to the sound card. From there you can add like a master limiter to control digital clips.

3. Add a couple other stereo busses and in one add a reverb, and the other a compressor. (Remember compression only need be light) This will make it easy to add a touch of whatever to each track.

4. Mix the panning and such and play to hear results. Make sure that the master buss is not in the red and only tags the yellow on occasions.

Do a mix down and allow dithering to 16 bits and see what you get.