My first suggestion is to read and study. There are literally hundreds of threads here regarding exhaust mods and about as many different opinions about recommendations. There is a tendency to take the first two or three replies to a new thread and assume that those replies represent the views of the majority of people here. That would be turning your hard earned extra cash over to pure random chance. Accordingly, I recommend you use the search function and do lots of reading before letting go of the cash.
My second suggestion is for you to let us know what your modding goals are. Is it appearance? Is it sound? Or is it power? Because it is going to be somewhat hard to find a single answer that will address all of these issues equally well. And two of the three, appearance and sound are purely subjective. The answers you are likely to get will be in the nature of whether you prefer blondes, brunettes or redheads, or what skin complexion or body shape you prefer. The answer will be true for the person giving the preference, but may not be what you are looking for at all. See what I mean? When it comes to appearance or sound, you have to go with what YOU want, not what we suggest.
The one parameter that can be objectively measured is the power objective. We do know that the stock CBE is extremely high flowing on the first generation MS3. While this may not be true on other cars, on the MS3 the CBE design is damn near perfect from the standpoint of power production. Rare for a factory exhaust. It flows so well, that you will not see a meaningful gain in power with ANY aftermarket CBE unless and until your other mods get you above 300 wheel horsepower, which is extremely difficult to do on the stock K04 turbo. Typically, no aftermarket CBE will produce significant gains until you go "big turbo" and are otherwise fully bolted. Yes, the stock CBE is that good. Changing to an aftermarket CBE just changes the sound. What sounds pleasant to one person may be bad noise to another.
There ARE severe power-robbing restrictions in the stock exhaust system, but they are all UPSTREAM of the stock CBE. They are in the stock downpipe which has a very sharp, pancake right angle design and a restrictive low-flow catalytic converter. There is also a low flow secondary cat in the separate stock mid-pipe section right before the CBE.
There are a number of good approaches to resolving these restrictions and getting a good bump up in power. Again, the solution will depend on your goals and the legal climate where you live. Does your state do emission testing? If so, you'll have to have some kind of cat in the system. If they just do a tail pipe "sniffer testing'" you have several good aftermarket options with high flowing catted downpipe and open race pipe or catless downpipe with a high flow cat put in the racepipe, etc. If you live in a state like mine where no testing is done, you can go fully catless, as I have done. There are some potential issues relative to each of these options, but that is beyond the scope of this response. If you are in a state where there is a physical inspection and the install has to be stock or look like it is stock, then I would defer to those members here who have developed some type of solution. I don't know.
What I can say is that if you can go with a good bell mouth shaped 3 inch downpipe or a divorced wastegate design downipipe and run catless or with a single high flow cat, you can probably pick up 20-25 horsepower with this mod, and combined with a good intake, either SRI or CAI, pick up on the order of a total of 40-45 whp, which is significant. And these gains are not "peaky" or only in one part of the power band. Removing those upstream restrictions produces a very broad, flat and fat bump up in power all across the usable "on boost part of your power band from 2,700 rpm up to your shift point of 5,500-5,800 rpm.
If you are more interested in appearance and sound, I can't help you much. Nor do I think that sound clips are very helpful, because they simply will not sound the same through your speakers, and the quality of cell phone or microphones and recorders used to make the clips vary so widely that the differences in recording equipment may be more pronounced than the differences in the exhaust systems themselves. You have to hear the exhaust on a real car and you also have to know what other mods the car has. Changes in other parts of the exhaust system, such as different downpipes and sometimes even different race pipes can change the tone and volume of the exhaust.
I hope this is a start. Search, search, search. If you have trouble with the search function here, may I offer this suggestion: Use Google search. Type in "mazdas247" (without the parenthesis) followed by your search terms. Google will direct your search to this site, but use its own search protocols to produce a list of "hits" for you to check out.
