This has beed discussed too many times. Please refer to the working projects in the threads below.
The issue with Filter-DMA-VDAC transfer is that the Filter output is signed (int8), while VDAC8 input register accepts only unsigned values (uint8), so some workaround is necessary. If interrupt polling technique is used, then value can be simply incremented by 128u. But no such luck if DMA is used. For that reason either intermediate logic can be used (to XOR highest bit), or ADC input should be limited to a half-range, like 0-to-Vref, or Vref-to-2Vref.
Thanks for your help...the example is working now