The Emperor of Eternity, unfortunately, didn't really satisfy me. It's a straight historical tale of Two, Jamie and Victoria ending up in the China of Emperor Qin in 210 BC, penned by Nigel Robinson who is rather far down my list of favoured Who writers. His prose is not as flat here as it sometimes has been, but he clearly doesn't understand how to write for audio - dramatic incidents happen off-screen, peculiarly paced switching between direct and indirect speech, and also totally fails to convey the on-screen characterisation of the Tardis crew - I'm in the middle of the Victoria stories at present in my rewatch, and basically Robinson makes Victoria too stupid and Jamie too smart. In the extra track, Deborah Watling tries almost successfully to convey that she understood what was going on, while the production team compliment Robinson on how well he conveyed the sort-of samurai setting (further comment unnecessary I think).
The Architects of History is a decent close to the story of Elisabeth Klein, who we last saw trying to rewrite the ending of the second world war to suit herself; Stephen Lyons is a generally solid-to-good writer who invented her in Colditz in the first place, and now gets to bring in both some aliens called Selachians which he apparently had previously used in two Second Doctor novels (must try and get hold of them). The second best thing about the story is the intricate way in which Lyons sets up various alternative histories across which the Doctor and Klein are variously plotting (he reflects on the extra track that Star Trek: Voyager over-used this plot, which I must admit I was unaware of); the best thing about it is the way he personalises it with Lenora Crichlow of Being Human as a Seventh-Doctor-Companion-Who-Never-Was - very difficult to make us care about a character who is introduced to us as having loads of back story which we have never heard of before (and may never hear of again), but between Lyons' script and Crichlow's performance they pull it off.
Though I have an odd complaint - some of the guest cast are really very flat in the first episode or so, as if they hadn't really read the script properly or just that the recording booth was not comfortable. They warm up as it goes on, but it's unusual enough for this to happen in a BF production that I noted it.
In summary, The Emperor of Eternity is not strongly recommended, while The Architects of HIstory is a satisfying conclusion to the Klein arc but may not make much sense if you haven't hear both Colditz and Survival of the Fittest.