If the Shaliach Tzibbur for maariv (outside of Israel) goes too quickly for me to start the Amidah with him, is there a source which would allow me to omit the section ברוך השם לעולם אמן ואמן? This assumes that I could not have started maariv before the shaliach tzibbur and catch up that way.
I was advised many years ago by one of my Rabbeim to skip it if, as is usually my situation, I would be unable to finish in time to start Shemoneh 'Esreh with the Tzibbur. I was also advised (when I asked someone else several months later) that it is not possible to make it up afterwards - in case you were wondering. I believe the reason for the latter point is that it is a Berachah HaSemuchah LeḤavertah. The original point, I believe, is as Ariel K stated, that it interrupts Semichath Geulah LiThfillah and is not recited at all in many congregations for that reason.
Tefillah btzibur by maariv takes priority even over semichas geulah ltfillah (saying shema and its brachos before shemoneh esrei), so it obviously takes priority over "baruch Hashem..", which according to many sources should not even be said lchatchilah.
I also don't think you should not start maariv early just so as to say "ברוך השם לעולם ", since then Bar'chu will not be next to birchos kerias shema. You should only start maariv earlier if you won't be up to shemoneh esrei at the same time even with omitting "baruch Hashem..".
More on ברוך השם לעולם :
It is a controversial bracha since it is not one of the brachos instituted by chazal for birchos kerias shema. It seems it may 'mess up' the number of 7 total brachos they instituted for shema. It also seems to go against "semichas geula ltefillah" since it separates between "ga'al yisrael" and shemoneh esrei. Many rishonim have discussed its status and whether it should be said or not. While many have the custom to say it, it should not be confused with the obligatory brachos and shouldn't take priority over universal halachik rules.
In order to undersantd this answer, we have to understand that maariv is not a single prayer, but a set of connected units:
- Krias Shema
- Birchos Krias Shema (SA OC 60:2)
- Shmona Esre (Brachos 4b)
Baruch Hashem/bircas hayira (Pashut)
Birchos Krias Shema and shema are said together lechatchila (see, for example Aruch haShulchan OC 58:19)
Geula is lechatchila connected to shemona esre (as opposed to tefilos b'emtza tiknum).
- Baruch/yir'u, originally a takana but now a minhag, was kept in its original place and did not pose a geula-tefila connection problem because it involves geula (Aruch haShulchan OC 236:8).
When the institution of tefila b'tzibbur collides with the above institutions, sometimes tefila b'tzibur wins, sometimes it doesn't. It trumps the geula-tefila connection and the minhag of baruch/yir'u. It cannot break up the unit of birchos krias shema.
When you are in a hurry to daven tefila b'tzibur, you are not "skipping over" birchos krias shema, you are merely disregarding the geula-tefila connection. When you skip Baruch/yir'u, you are literally skipping it- the minhag is to say it like the original takana and that is exclusively right after bichos krias shema (Aruch haShulchan 236:13).