Alekmaul has just released his MAME EMU for the DS2.

You need MAME ROMS which are compatible with MAME 0.37b5. This is a relatively older version. Many of the later version MAME roms will not work. Some ROMS can be easily converted (using freely available tools), others cannot. Later versions of MAME tend to concentrate on compatibility as the cost of performance. Earlier versions are more in line with the hardware capabilities of our target machine. These earlier versions have some significant programming speedups which have been removed in later versions. Two examples are the use of internal 8-bit graphic rendering and dirty buffer handling.

Later versions of MAME with ALL the drivers included can easily reach a size of 40-60MB - more than the amount of RAM available to the SCDS2 (which is 32MB). So basically we're talking trade-offs here.

Source- potabledev