From a visual point of view, the best way to do the conversion from 23.976 to 25 is to speed up your footage: instead of playing 23.976 frames per second, you are playing your program at 25 frames per second. Obviously they are disadvantages with this method, one of them being the sound pitch changing. Some software allows you to compensate somewhat for that. I am guessing that might be an issue for your concert recording. The other problem is that if you have a requirement for the finish length of your master, now your program is shorter!
Speeding up your program is pretty straight forward: using Cinematools or Quicktime Edit (Digital Rebellion) you just need to change the flag of your Quicktime movie to 25fps (make sure you make a copy of your 23.976 master first!)
Regarding the interlaced requirement, this is part of the broadcast standard (US and Europe) for HD 1080 show: Just use Adobe Encoder or Compressor to make an interlaced version of your show from the progressive version.
HTH,
David Baud
Post & VFX
KOSMOS PRODUCTIONS
Denver – Paris
http://www.kosmos-productions.com