How to count beats in acapella and slow music??

Hello all, I am new here seeking help to learn how to count beats in acapellas, intros and slow music for DJing purposes to do beatmatching. I can locate the first downbeat [kickbass] in tunes so I can account for the 4 beats in a Bar.

Problem I am having is when I need to match beats with intros, acapellas and slow tunes, if anyone can help or refer me to an appropriate forum for this will be greatly appreciated, thanks.

Is there a particular example you're working off of?

Thank you. Maybe we can start with a very loooooong intro like Diana Ross's I'm coming out if you won't mind.? If yes, I don't know how or where we can work off the tune itself. To clarify, since I match the first downbeats of any 2 tunes, that is what I would like to know, how to recognize the 1st downbeat in any intro, acapella or slow tune?

Are we listening to the same "I'm Coming Out"? It's a pretty upbeat song the whole way through. 

Yes it is but seems no one can answer the basic question on how to counts beats in an acapella.

Then your reference didn't match your question.
To your question, you need to go to a part of the song where there's more going on, since acapella music is notorious for switching tempos all the time and start tapping from there. If by chance the entire song is sung homophonically, you can internally subdivide beats closer and closer to where you can get 2 or 3 or 4 consistent beats between two musical moments.

https://www.youtube.com/watch?v=uli4qfH07Io

In this song, for example, since it starts on a pickup it can be harder to find beat one, but starting to count internal beats from the first half note, would yield a 4/4 time at about Q = 70. This particular recording slows down a lot so you need to subdivide the beats further and further to find that steady pulse, even if it is shifting.

Whoa, that's really very in-depth details, way beyond my scope and yes good acapella to reference my question.

There is an automatic beatmatching DJ software called Mixmeister which perfectly matches any intro or acapella to a tune. I was always confused how this software can do this so have always thought the software was finding a beat in the intro/acapella.

A simpler way of saying what I'm saying is find a place in the song where the beats are much more stable (if it's a good song, there will be at least one), then go to the beginning or any parts that slow down and see if the tempo and time signature you found fits as a base, unless of course the song changes tempo markings within the song, not just slows down. A lot of software analyzing these things has a tendency to oversimplify the issue. I was making a mashup one time and found that despite the program telling me my second song was Q = 97, it slowed down ever so slightly within the song, making a perfect sync much more difficult. 

Aside from being a composer, are you also a DJ? Reason asking, it's mainly DJ's who use Mashups and yes, technically that is what I am seeking to do. Would you mind if I were to send you 2 mp3's then maybe you can tell me how the DJ was able to do that mashup please? If yes, I can send you 3 files, the mashup itself and the 2 individual tunes used. If so, you can let me know how to get those 3 mp3's to you.