First and foremost, without a fully open back, you need to get the front venting model, either the S or the T series.
Top or rear venting will do you little good.
I know firsthand with the T series that there is an alarm feature that will notify you if there is a mishap. I also leave my display on and can see the temperature even when not using my gear.
I am not certain what the differences are between the S and T series, but I do know the T Series works well. I have the front venting T-10 because my Marantz was in a cabinet for a while, and even with all the recommended space above/behind/both sides, it still got toasty. Until I got the t-10 set up, that is.