A: SB PCI512 MIDI Synth
B: SB PCI512 MIDI Synth
These are the synth chips on the card. Having two, each of which can respond to up to 16 MIDI channels, is how you get 32 voice polyphony out of the card.
SB PCI512 Soft Synth
This is a software synth that Creative supplies.
SB PCI512 MIDI UART
This is simply the MIDI port on the SB card. If you sent the output of a track here it would go out the interface via a MIDI cable to an external device. UArt (pronounced u-art) is short for universal asynchronous receiver-transmitter. It's a computer component that handles asynchronous serial communication. Every computer contains a UART to manage the serial ports, and MIDI interfaces have one as well.
Aark 24
MPU-401
Is there really a MIDI device just labeled "Aark 24?" Or did you mean that there's one labeled "Aark 24 MPU-401?" This would be the MIDI out port on the Aardvark card. MPU-401 is the designation for a particular implementation of a MIDI interface designed by Roland that became a defacto standard. It has two modes, an "intelligent" mode and a "dumb" UART mode. Most cards that have a MIDI interface implement UART mode only.
Microsoft GS Wavetable SW Synth
Microsoft MIDI Mapper
The first of these is a softsynth that comes along with Windows. The MIDI Mapper is a utility that allows you to create a mapping of MIDI messages from input to output. That is, you can transform the messages. This might be useful if you had some old MIDI gear that was not General MIDI-compliant and you wanted to map the MIDI messages from a GM sequence to the appropriate equivalents to use the old box as if it were GM-compliant.