The best areas are past the last button lifts, up the gondala top. Also you can take a snowcat up "Musala", the highest peak in the balkans, will cost you 40 lev.
I went to Boro on 28th jan, off piste conditions were pretty difficult. Hard crust with deep heavy snow underneath. But I thinks its snowed quite a bit since then, so maybe its improved.
Thank you very much Garry for actual information. I am going to Boro on thursday 16 and i heard that its snowy now. Hopefully i will get a chance for powder riding.