As noted, you have very nice flagship class AVP and power amplifier, so it may be worth for you to understand the impedance and phase angle curves so that when you are ready to upgrade your speakers, you know what to look for, in order not to put your very nice but expensive equipment at risk unnecessarily.
Below is such a graph, but they are for the S2, so your S3 will have different characteristics, that could be very similar. So, let's assume they are similar enough and you can see the following potential concerns:
The solid curve is impedance versus frequency, and the dotted one is phase angle versus frequency.
- If you draw a line at 4 ohm, it is obvious that at between around:
85 and 195 Hz, 510 and 880 Hz, 1200 and 40,000 Hz, impedance dip below 4 ohms
- For much wider bands, impedance drops below 6 ohms
- At around 88 Hz, the phase angle is about 88 Hz, such large phase angle would cause much more heat dissipation in the output stage of class AB amplifiers, but likely much less so in class D amplifiers.
So, that's why John Akinson noted the following:
Gene, and some of us are suggesting that when using BTL, at the same output power, the current would be 2X that for "normal" connections, and that's why it is not advisable to use such configuration with 4 ohm nominal speakers.
Your speakers, if the curves are the same or similar enough to that of the S2, then it is not really 4 ohm nominal, but it does dip below 4 ohms in the range mentioned above.
That really isn't a huge concern because music contents and movie sound tracks don't play pure tones, so the chance for contents to demand the amplifier to play at those frequency dips will mot likely be for very short duration. Any decently designed power amplifiers can sustain much higher current for short durations.
The phase angle is also not a huge concern because it does not really result in higher current, that lots of internet forum members might think it would, because of Stereophile's undue (imo only) emphasize on their term know as EPDR (equivalent peak dissipation resistance). That term, while useful as it can be used conveniently to assess the effects of phase angle effects on power amplifiers, it also tend to mislead forum members who may not have deep enough understanding of electrical principles.
Regardless, in this case the "DPDR" will not be much lower than the 3.1 ohm dip anyway so let's not worry it. I just want to mention it, because sooner or later someone may throw that term of you and might care you (just ignore them if and when they do, take it as a cautionary note but not more than that).
In summary, you can see that base on your speaker's characteristics (being similar to the S2), and the fact that it really can' take more than 300 W continuously anyway, even if you leave it on BTL mode, there is no need to lose sleep over it. Our (assuming others agreed) suggestion of selecting "normal", or "Biamp", is just cautionary, as Gene alluded to, he would have no issue doing it, but wouldn't tell others to do it.
If and when you are ready to upgrade to speakers such as the KEF reference, and/or B&W's 800 diamond series, then you do need to pay more attention the impedance/phase angle curves, versus you Amp 10's capability. For the 702 series, just sit back and enjoy, as you alluded to, you never push the volume thing too hard anyway so do whatever you like, any mode selection should work safely (just that normal mode is even safer) for your application/speakers.
I hope this long post clarifies things enough for you.
Bowers & Wilkins 702 S2 loudspeaker Measurements | Stereophile.com
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