ID'ing the Hiring Manager

I am in the process of applying to equity research positions. I have found that directly contacting the hiring manager is the most effective way of getting my resume noticed. For the sector that I am most interested in, I can often determine that the hiring manager is one of 5-6 different senior analysts, but cannot for sure figure out whom among that group is the correct person to contact. Calling has not helped since I just get redirected to the HR department's black hole of resume death.

Is it appropriate to send an email to all people from my short list? My network has given limited help in determining who to contact since often times these companies have a limited number of for example fellow alumni working there.

The way I see it I have several options. First, is to send cold emails to lower level associates and try to network up through that means. Many are similar to myself in that they have an advanced degree/industry experience that was leveraged to receive the position, so we have a common talking point. This approach, however, may take more time and could result in the position being filled before I get the desired info.

Second, I can send cold emails to all of the senior analysts who are on my short list. I would tailor the individual emails somewhat so that they do not all come off as copies where I have just changed the name of the person being addressed. I am worried that both kinds of carpet bombing approaches may be a put-off.

Any advice is appreciated