The only real "Broadcast" Betacam SP decks were the BVW series. They have much better dropout compensation than the PVWs and UVWs, and they have better picture quality and less other problems. The UVWs never were able to record or play back the audio channels 3&4, but for the PVWs (at least for the 2800) there was a modification that allowed to record and play back the channels 3&4. For the first PVW we got we bought this modification; it added one additional HU on top of the deck with extra VU-meters and knobs, plus extra inputs on the back for the additional channels, plus some additional internal modifications to make the image more comparable with something a BVW would deliver.
Note that the channels 3&4 on Betacam SP are embedded into the video signal. This means that you cannot record on Ch3&4 without recording video, and it means that as soon as you record video you are recording audio channels 3&4 at the same time.
I would recommend either renting a BVW deck for mastering, or finding someone with a Media 100 and a BVW deck that can play out your material e.g. from a FireWire drive for you. For German TV stations it was never officially "allowed" to work with PVW or even UVW decks, and admitting not to have a BVW and doing broadcast work would never have been an option. These days they expect DigiBeta tapes and nothing else (okay, maybe HDCAM and HDCAM SR); and since we want to work in Broadcast we have to follow their rules.