This might be of use. It does not discuss the views of medieval Muslim scholars on democracy itself, but it shows that they were (at least those that are mentioned) influenced by Plato. Which means that they weren't favorable towards democracy. They were elitists for the most part. Governance is for the special few, the many should be governed. Athenian democracy on the other hand is about self-governance and autonomy; citizens, not philosopher kings, ulama, tyrants or God, decide the laws by which they will govern themselves. Now, even if a Muslim scholar was to interpret ijma (consensus) broadly, pointing to a consensus among all Muslims (and not, say, just scholars), and argue that this is how decisions should be made in a Muslim polity, it would still be somewhat different to the Athenian democratic experience, since, most probably, the consensus of all Muslims would (be said to) reflect Sharia or God's will, whereas consensus in Athens reflected the citizens' will. The source of legitimacy is different even if in practice it is always the people governing themselves.