En cuanto revisemos la mezcla, difundiremos la cabecera.

Because en cuanto triggers the subjunctive when it refers to something that has not happened yet.

In this sentence, the review of the mix is still in the future, so Spanish uses:

• en cuanto revisemos... = as soon as we review / have reviewed...

This is a very common pattern with time expressions such as:

• cuando
• en cuanto
• tan pronto como
• hasta que

When they point to a future action, Spanish normally uses the present subjunctive, not the present indicative.

Compare:

• En cuanto revisemos la mezcla, difundiremos la cabecera.
  Future, not done yet → subjunctive

• En cuanto revisamos la mezcla, detectamos un fallo.
  Habitual or general situation → indicative

So the subjunctive here does not mean uncertainty in the English sense; it is mainly about the action being pending/future.

Here, en cuanto means as soon as or once.

It introduces a time clause and emphasizes that the second action will happen immediately after the first one.

So the structure is:

• En cuanto + subjunctive, future main clause

A very important warning for learners:
en cuanto is not the same as en cuanto a.

• en cuanto = as soon as / once
• en cuanto a = as for / regarding

For example:

• En cuanto llegues, te llamo. = As soon as you arrive, I’ll call you.
• En cuanto al presupuesto, lo revisamos mañana. = As for the budget, we’ll review it tomorrow.

That extra a changes the meaning completely.

Because the sentence is talking about a future result:

• first, we review the mix
• then, we will release/distribute/broadcast the opening sequence

So difundiremos is the simple future of difundir.

Spanish often uses the simple future in this kind of sentence because it sounds clear and neutral:

• En cuanto revisemos la mezcla, difundiremos la cabecera.

A more colloquial alternative could be:

• En cuanto revisemos la mezcla, vamos a difundir la cabecera.

That is also valid, but difundiremos is perfectly natural and slightly more concise or formal.

Sometimes yes, but the future is the safest and most standard choice here.

Spanish often uses the present to talk about the near future, for example:

• Mañana publicamos el vídeo.

But in a sentence like this, with a future time clause introduced by en cuanto, the simple future sounds especially natural:

• En cuanto revisemos la mezcla, difundiremos la cabecera.

Using the present in the main clause could be possible in some contexts, especially in informal speech, but it may sound more like a scheduled action than a straightforward future consequence.

So for learners, the most reliable model is:

• en cuanto + present subjunctive
• future in the main clause

Because Spanish usually leaves subject pronouns out when the verb ending already makes the subject clear.

Here:

• revisemos already tells you the subject is we
• difundiremos also already tells you the subject is we

So nosotros is unnecessary unless you want emphasis or contrast.

Compare:

• En cuanto revisemos la mezcla, difundiremos la cabecera.
  Neutral, normal

• En cuanto nosotros revisemos la mezcla, difundiremos la cabecera.
  Emphatic, maybe contrasting with someone else

English needs we, but Spanish often does not.

They come from two different verb forms.

1. revisemos
This is the present subjunctive, nosotros form, of revisar.

Steps:

• infinitive: revisar
• present indicative yo form: reviso
• remove -o → revis-
• add present subjunctive ending for nosotros in an -ar verb: -emos

Result:

• revisemos

2. difundiremos
This is the simple future, nosotros form, of difundir.

For the simple future, Spanish adds endings to the whole infinitive:

• difundir + emos → difundiremos

Other future endings are:

• -é
• -ás
• -á
• -emos
• -éis
• -án

So:

• difundiré
• difundirás
• difundirá
• difundiremos
• etc.

Very likely, yes.

This sentence sounds as if it belongs to a media, audio, video, or broadcasting context.

• la mezcla often means the mix, especially in audio production
• la cabecera in Spain can mean the opening sequence, title sequence, or intro of a programme

So although both words have broader meanings in general Spanish, here they probably sound like industry vocabulary.

For example:

• mezcla can simply mean mixture
• cabecera can mean header, headboard, or other kinds of heading/head section

But in Spain, in TV/radio/video contexts, cabecera very often refers to the opening part of a programme.

That is why the sentence may sound slightly specialized rather than everyday conversational.

Because the sentence begins with a subordinate time clause:

• En cuanto revisemos la mezcla, ...

Then the main clause comes after it:

• difundiremos la cabecera.

In Spanish, when this kind of clause comes first, a comma is normally used to separate it from the main clause.

So this is standard:

• En cuanto revisemos la mezcla, difundiremos la cabecera.

If you reverse the order, the comma is usually not used:

• Difundiremos la cabecera en cuanto revisemos la mezcla.

Both orders are correct. The version with en cuanto first slightly foregrounds the condition/time trigger.

Yes, you could say cuando revisemos, and it would still be grammatically correct.

However, the nuance changes a little:

• cuando revisemos = when we review
• en cuanto revisemos = as soon as we review

So en cuanto suggests more immediacy. It sounds like the second action will happen right after the first one.

Both would still take the subjunctive here because the action is in the future:

• Cuando revisemos la mezcla, difundiremos la cabecera.
• En cuanto revisemos la mezcla, difundiremos la cabecera.

The second one is more precise if the idea is immediately after.

Yes, absolutely.

That version is fully correct:

• Difundiremos la cabecera en cuanto revisemos la mezcla.

The meaning stays essentially the same. The difference is mainly one of focus:

• En cuanto revisemos la mezcla, difundiremos la cabecera.
  Emphasizes the time trigger first

• Difundiremos la cabecera en cuanto revisemos la mezcla.
  Emphasizes the main action first

This kind of flexibility is very normal in Spanish. The verb forms do not change:

• revisemos stays in the subjunctive
• difundiremos stays in the future

Only the information structure changes slightly.