Without the bootstrap, each 470 pF cap has an impedance around 16 kΩ at 20 kHz. This makes the CM input impedance of the circuit 1,000 times lower than it is at mid audio frequencies. This makes CMRR exquisitely sensitive not only to source impedance imbalances but also to the matching of those capacitors - even if the driving source had perfectly matched 50 Ω impedance in each leg. Remember that to get a 90 dB CMRR figure, the impedance of the two lines must match within 0.01% or better. But the imbalancing effect on the receiver's own CM impedances can be reduced by effectively reducing the capacitor size (raising it impedance) by bootstrapping. I don't recall the exact numbers, but the bootstrap reduces the 470 pF down to the area of a few pF in the audio frequency range, making their impedance rise to over 1 MΩ. So they make the degradation of CMRR due to source impedance imbalance at 20 kHz roughly comparable to the 10 MΩ figures at mid audio frequencies. One of the side effects is that a 5% tolerance at 470 pF has about 100 times less effect - making its effect on the circuit about the same as if it had 0.05% tolerance. There's a lot more to the circuit behavior than meets the eye ... and, as I've demonstrated here, it's also hard to explain. But, under identical conditions of source impedance, the InGenius circuit will, above about 5 kHz, have better CMRR than the best of Jensen's input transformers. The THAT website has some good references explaining why extremely high CM input impedances (10 MΩ) work to vastly reduce the CMRR-degrading effects of source imbalances. It's nearly 1,000 times less sensitive than an ordinary diff-amp built with an op-amp and matched 25 kΩ resistors. The bootstrapping of the RF filtering capacitors is a way to add RF attenuation while keeping the CM input impedances very high.