1. The TT2 is an excellent DAC on it's own. The M-Scaler can bring improvements to many DACs...1) even though the tt2 is well loved, the tt2 (only?) really shines with the hms;
2) the usb is not as good as the optical input. i am using usb out from my imac at the moment;
3) i may need to look at RF issued and look at an external battery, or is that more for the hms. Does rob watts not believe so - I haven’t totally to understood the (maybe) difference in opinions;
4) upgraded bnc cables are highly recommended for the hms tt2 link.
2. I use USB and it's galvanically isolated. There's nothing wrong with USB in my opinion BUT I am not using a Mac as the source (my source also has galvanically isolated USB).
3. TT2 is fine with the standard power supply.
4. I recommend them but they are the icing on the cake (or the glaze on the icing on the cake as I seem to remember Rob Watts saying). Certain cables will help with RFI.