And then there's the fourth way, which I think may be the most common: use an operational amplifier. ("Op-amp.") They can be fully discrete, and seem to be the approach used by many, such as ARC, for example.
@cleeds Opamps can generate a balanced output easily enough, but not one that is floating. The output of any opamp is single-ended, so to hear it, the other connection is ground. So to do a balanced output, you'd need at least 2 opamps, each generating a single-ended output, one out of phase with the other. Each referencing ground, so no, this won't support the standard. But it is balanced. An output transformer or our direct-coupled output section both produce an output that is floating.
To use a chip based solution, you need something like this, a balanced line driver IC, which is also floating.
I agree with you that internal components are critical but I posit that the external components, such as cables are also important.
I recall a discussion in the 90s about speaker cables. The question was most speakers used cheap, thin wire internally to the drivers as well as fairly inexpensive components in the crossovers. So what was the point of buying expensive speaker cables?
To be clear, I've never stated that speaker cables are not important. They are, IMO, IME. Because they can be critical (especially if you are running lower impedance loads, like 4 Ohms) its best to keep them as short as possible. To this end I keep my amps right by the speakers and run long interconnects. That way I can have the equipment stand for the front end of the system where I want it rather than forced to sit between the speakers. Since RCA cables can and do impose a sound of their own (which is bad) to minimize colorations due to cables, having long balanced interconnects and short speaker cables makes a lot of sense, especially if the associated equipment supports the balanced standard.
