Note that the Sounblaster PCI 128 (ens1371) does not have a synthesizer on the card. This was not obvious to me when I bought mine :-). The talk of "creative synthesis engine" is a software synth which is installed with the windows drivers. This means that it cannot convert midi files, or midi streams, on the card. It does have a midi connection so you can connect external Midi equipment to your computer if you would like.
Fortunatelly, you can use Timidity++ for to play midi files. See
There are two ambition levels for using Timidity++:and SB PCI 128 to do MIDI:
(1) you just want to play midifiles. (2) you want to use other midi intruments with your computer such as an external MIDI instrument that uses Timidity, or letting a program playing an external MIDI instrument. Or, you just want it to appear as your card does have MIDI support and any program that knows how to play midi using the Alsa drivers can work.
For (1) you just need to install timidity and use it as a midi file player. You do not need to configure Alsa to do any MIDI/sequencing stuff at all. You do not need to pass the '--with-sequencer=yes' to the configure script when you build the Alsa drivers, and you also do not need to load the snd-seq-oss drivers (for OSS compatibillity). Timidity is a program that reads an midi file and generates a sound file (PCM/"wave" file) which it sends to the sound card, just like your mp3 player reads .mp3 files and converts them to something that can produce sound on the soundcard.
For amition level (2) you can use Timitidy to "hook into" the Alsa midi drivers. This will make the Alsa midi/sequencer interfaces work as if there was a midi device on you sound card. For this to work you should run Timidity as an "ALSA sequencer client" using the "-iA" argument. This requires that Timidity is compiled with Alsa support (which it is not in my RedHat 7.2 installation). With this ambition level you should still build Alsa with the '--with-sequencer=yes' argument to the configure script. On the below web page you can find more info on how to run Timidity as an Alsa sequencer client.
Possibly this is valid for all soundcards based on ens1371.
Frans Ketelaars told me most of this when I sent confused emails to the alsa-user email list..