Hi Diki
Both Wersi OAS Arrangers and the Lionstracs Mediastation will do what you ask.
Info: OAS 7 has about 700 Mb of samples as standard, and they are loaded into Ram at start-up, the time taken from power on to full use (Load Windows OS, OAS software and the 700 Mb of samples) takes about 1 ½ minutes.
If you want to use Giga samples or VSTs then once again this is no problem as only the start of the sound needs to be loaded into ram, the rest of the sample is streamed direct from the hard drive.
Hope this helps.

Bill