It may (or may not!) surprise you to know that this is a very imprecise area of Intellectual Property law. At its heart is the question of whether a sample constitutes an infringement, and therefore whether or not prior permission is required to make what is called a derivative work, namely the DJ's mix. The law is vague and was written before the phenomenon of sampling was really recognised.The law says that if a 'substantial' part of the original work is used then this constitutes an infringement, but it will be up to a court to decide what substantial actually means in each case. For instance in one test case, the use of 12 bars of an original piece of music was considered substantial because the original piece (an item of music in newsreel film) was itself not very long. On the other hand, if you believe the PRS for Music site (
http://www.prsformusic.com/creators/wan ... mples.aspx)
all samples require the permission of the original copyright owner. Personally I would view this statement as being over-simplistic, especially as PRS has a reputation for aggressively pursuing its members interests.
So it will entirely depend on the amount of each sample contained in the mix(es) as to whether prior permission should have been obtained. If the mix is found to contain infringing amounts of other people's copyright material, there cannot be a separate valid copyright in the recordings of the mix released by the promoter (and he faces the possibility of both paying damages and having his stocks of the recording seized).
Let's assume for one moment that the DJ mix did not infringe any earlier copyright, because either the sample was small or the DJ had permission to use the sampled music. In a derivative work, the DJ as creator of that work would hold the copyright and he could assign that right to the promoter (ie transfer it absolutely) or he could licence the promoter to market the recordings but he (the DJ) would retain the copyright itself. Ideally such things should have been put down in a written contract, which you mention may have happened. A lot would depend on the wording of that contract in determining the promoter's legal position to enforce his agreement with the DJ over distrbution of the recording. If it was a non-exclusive licence, then the DJ might well be able to authorise others (for instance you) to also distribute his mix, although from what you have written it sounds as if the promoter was responsible for actually recording the mix during a live performance, so he may well own the copyright in the recording (as distinct from the performance by the DJ) and a second recording of the same live perfomance would be unlikely.
So following on from that background, I will try and answer your specific questions.
1. Assuming the DJ mix did not itself infringe copyright, then you would be infringing copyight in the promoter's recording if you distribute it via a website. Either the DJ or the promoter (depending on what they agreed at the time of the recording) could sue you. However, if the mix was itself held to infringe the earlier music which was sampled, then the DJ mix holds no separate copyright, and your use of it now would not be actionable by the DJ or promoter, but you could be subject to an action brought by one of the copyright owners of the original music (Winstons, Artist A etc).
2. Obviously whether or not the promoter was in breach (for distributing the recording) depends on whether or not the mix was itself an infringement. As he was the only person who actually seems to have made any money out of this project, it is more likely that the Winstons & Artist A or their management would be more likely to go after the promoter because an award of damages would be more likely if they won.
3. Assuming that the samples in the mix were 'substantial' then yes, permission would be necessary from the original artists or their agents. If you beleive that the DJ had verbal permission to use the samples, then a court might find that the mix was a valid copyright work, thus making the promoter's recording OK. But you would still need either the DJ's permission, or the permission of the promoter to publish the mix on your website.