Are Pre-Amps necessary?

This has been covered here on Audiogon many times before, again; it depends on the system.

^ This will only inform you as to how it works in your system(s).  Not necessarily as a general rule.

 Ideally you’ll have a DAC with extra available bits for volume attenuation, with a voltage output that matches the input sensitivity of your amplifier(s) for full output. Such a combination will allow for full power output capability of the amp(s) and full range of the volume control without the risk of bit stripping from the DAC. Appropriate interconnects are also needed.

Some DACs with volume controls have balanced outputs.

FWIW, and at the risk of appearing wishy-washy and probably not satisfying parties at either end of this discussion, I think both those opposing ends are both right.
 On the one hand, for some active line stages are liking rolling down hill with one foot on the accelerator and the other foot on the brake. Yet others are grateful that the accelerator is there at all.
 IMHO, most with existing systems will probably benefit from an active line stage. But, for those building systems, it would probably behoove them to seek out compatible gear that can do without an additional active stage. I’ve tried both ways in the past, and had a very slight preference for an active stage. But, I have confidence that with the more current available products that my future might very well be without an active stage, and I shop accordingly.

While I’m very much in favor of the consumer friendly policy of sticking to standards, I’m not sure that many of the benefits of balanced couldn’t still be realized if they weren’t exactly so.

I think the best way to delete the pre is to go directly from the source and avoid the additional passive volume control. In such a case, I don’t see why adhering to the balanced standard would be problematic unto itself.

Where I do see an issue with balanced, as opposed to single ended is at the amp inputs. Until amplifier manufactures adopt 2 to 2.2 Volt for RCA and 4 to 4.4 Volt for balanced input sensitivities for full power output. Many digital sources directly coupled to amps will often have to attenuate too much into many balanced amplifier inputs, and as such perhaps consequently run into a bit stripping issue. As it now stands, it might be better to sacrifice some of the advantages of balanced and use the RCA inputs. Hopefully this will change.

I think it behooves amplifier manufactures to adopt more complimentary standards for input sensitivities.