I have found no way to get around the lagging midis, so I'm using a more stable sound format like wavs or mp3s isntead. The way these different formats work is that they save sound frequencies and give that data to DirectSound which then gives it to the sound card in a format that the card understands, which then gives the data to the speakers which then spit out the pretty sound.
The problem with midis is that they do not save actual frequencies. You can think of midis as a musicial notation format. It saves what notes are pressed for how long, how they are articulated, and then they run through the same process, except DirectSound has to take longer with them because it has to convert all the notation data to actual frequency data.
Fortunately, I've seen many midi/music creation software that, after saving to midi, allows you to export to .wav or .mp3.
Mp3 is the most efficient format just because of the way its structured. I don't think it does too well with detail though because it crunches the sound data. Unless you're not planning to sell your game commercially, or at least not get too many customers, you will have to pay a royalty fee for using mp3s in your program.
Wavs on the other hand are the most accurate because it keeps track of everything, but has bigger file sizes and could slow your program down. Fortunately, there's no royalty fees.
Crazy Donut Productions
Current Project: KillZone