The previous post more or less confirms what I understand from a document issued by Price Waterhouse Cooper
This says that Bulgaria introduced anew accountancy act a while ago to bring things into line with the rest of the EU. Under this Act small companies only need to submit simplified accounts (as in the UK). These MUST be submitted though as this new act also increased fines for nonsubmission.
It makes sense that accounts can only be submitted online as this is much, much more efficient than standing in a queue for 2 or 3 hours as used to be the case years ago. There is a charge for submitting online however, this was 15 leva last time I heard. In addition an electronic signature is required and this has to be bought.
As regards POAs: you must sign one in front of a notary in order to give your accountant authority to submit your accounts.
If you can't do this because you are not in Bulgaria your accounts can still be submitted but by a lawyer, not by an accountant. In my experience most accountants work with a lawyer to do this.
All-in-all, I think the 50 leva that my accountant charges is well worth it.