questions about mp3 player ability

I am trying to make my own mp3 player using the arduino. I made the wav shield and thought it was really cool but i did not like the fact that it couldn't play mp3 files so i was thinking about using the VS1011e mp3 decoder chip.

I am looking at the pin descriptions for the chip and i have a question about the SCI(serial command interface) and SDI(serial data interface) ability of the chip. The documentation has options for both the SDI and SCI pins, it looks to me like i dont need all of those pins so i can use pull up/down resistors when not using them. I know i need an interface for the chip but i dont need any controls yet so i was wondering if i could just leave the SCI pins out of my first prototype shield and just use the SDI pins for an interface for now for transffering the mp3 data.

Would there be any issues with the arduino or software if i were to do that since this is using an SPI interface or am i safe to just use the SDI pins to transfer the mp3 data and then disconect the SCI pins for now and have them w/ pull up/down resistors.

Also would it be simple or very complex editing the sample sketch they give you for the wav shield to pull mp3 files instead of wav files and send the data to the correct pins?

If some one could give me some insight into what i am getting my self into that would be great thank you!

should be very straight forward as you already have all the file I/O in the wave shield project/library. Have a look at AVR Butterfly MP3 for an example ( not arduino but could be helpfull to read through. Also try www.yampp.com )

You will probably need both command and data busses on the chip to configure it for the correct crystal. It is not had to use both these on the same lines and and use the BSYNC line to differentiate between data and command. When the chip powers up it has a default setting which may be fine but if not our mp3s will sound wrong ( too slow or too fast or not at all )