The CL goal isnt impossible but if a BG team is to make it(95% this would be either cska or levski), it would be an entering from the type of Artmedia. The truth is that the BG teams do not have the strong mentality of the big Serbian or Romanian teams who, although sharing similar economic circumstances, have better successes overally. The main reason for this is the fact that before 1989, when the gap between east and western European clubs was much narrower, many eastern European clubs achieved some remarkable things, including reaching final and possibly even winning it. At the same time the greatest ever success(by cska) in a Euro tournament are semi-finals. So even then, results point that BG clubs were missing something and thats become quite acute nowadays when a slightly stronger opponent often makes the mentality of the BG club to shake.
But to go back to the issue...BG team is the CL group stage? Two ways for that 1) Good draw(tough luck for cska this year) 2) The BG club has formed a decent team that make a few games of their life vs decent opponents,like the 5:0 win by Artmedia vs Celtic(though for this one you gotta hope that the opponent team isnt in top form too). I personally dont care whether a BG team would make it to the CL because they dont really belong there. Over there are corporation types of clubs while,sadly,the BG clubs dont "quite" behave like companies yet...well, some of them couldnt anyway.