Hi,
If DMA is not getting started, do you see any error in the DMA status register? One thing I suspect is that, buffer submitted to DMA is not properly aligned as per the MSIZE configuration. You are using MSIZE=32 bytes (20H), so your buffer should aligned to 32-byte boundry. e.g. at address 0x00, or 0x20, or 0x40....so on.
I think, you can make sure that by adding following pragma before buffer defination.
#pragma align 32 unsigned char Tx_BUFF[BUFF_SIZE];