Before I even tackle Daniel's question...
Kristina and Jenni, thank you for the compliments.

Yes, I realize that they're very hard for you, Jenni, so please don't feel obligated just because I think Caleb is EXTREMELY handsome. :lol: And Kristina, Jaeger is very tolerant...NOW. Perfect segway into Daniel's question.
I don't think Jaeger and Dom both being male had much to do, if anything, with how well (or how quickly) they became acclamated to each other. At the age we brought Dom into the house, HE didn't even know what he was, I don't think

lol

, let alone Jaeger! If he'd been older, then yes...bringing a new male into the house would have concerned me, as Jaeger is very dominant.
Either way, the first few weeks we had to supervise them VERY carefully. Jaeger was far less tolerant than he is now. He was jealous of every second of attention that we gave Dom, and all of the toys in the house were HIS. No sharing. Several times he bit Dominic fairly hard, even drawing blood once or twice, so I really had to step in and say, "Hey, I'm the boss around here and you WILL play nice". Of course, every time I did that, I honestly thought I was going to lose MY arm... 8-[ It was a huge transition, and Jaeger's personality changed dramatically for quite a while. I even considered getting rid of Dominic if it didn't improve.
Then one day, out of nowhere, they just started playing. I'd say it was maybe 3 weeks after we got Dom home? Maybe a little less?
Even so, I still had to limit their playtime to 5 or 10 minutes at first and I had to force Jaeger to lay down the entire time. He'd get WAY too excited, which led to him getting WAY too rough, and Dom would wind up scared and under the kitchen table.

Then their play progressed to the point where he could stand up and bounce around Dom without Dom running away, although he was still noticably nervous. Finally, they got to the point they're at now - they can do pretty much anything to each other and it's all in good fun. =D> And Jaeger is extremely protective of Dom when we're out.
There's still no question about Jaeger being the dominant one in the house (although I have a feeling that will change eventually), but he's fair now, at least, and Dom has learned that the only thing "off limits" - PERIOD - is Jaeger's food.
The point of my rambling is that supervision, at least for a few weeks, is of upmost importance, and you have to (quickly) make sure that the older dog understands that aggression will not be tolerated, IMO. Especially since a puppy's character can be so influenced by the experiences he or she has during those first few months. And I'm sure we didn't go about this whole thing "correctly", either, but our facilities are rather limited.
Simba is probably young enough that you won't have too much of a problem with aggression - he probably would see a puppy as a playmate rather than a rival - but I guess every dog is different.
Hope that helps.
Oh, and Stacia is absolutely right - MOVE YOUR BREAKABLES! :lol: Destructive is an understatement! :lol: