Most SS sources (excluding tube ones) have an output stages that can equal and sometimes better many preamp output stages, especially tube ones.
So the myth that a preamp can drive the interconnects to the amp better is a "furphy", and started by preamp manufactures, and "Ohms Law" will prove that time and time again.
The only time you may like a preamp in the way is if you prefer it's colouration it gives, at a cost of transparency.
The second statement in the above post is not supported by the first statement. The reason to go with a preamp, or to go without one for that matter is to get rid of coloration.
So which is it?
The problem is *not* whether a preamp can do a better job driving an interconnect cable than a source can, the problem is actually can the source control the interconnect cables in such a way that the cable *after* the passive volume control (the one that connects to the power amp) won't contribute artifact.
If you have ever wondered why a passive only sounds right with the volume all the way up, this is why. The source can control the interconnects within its abilities if the passive is turned all the way up. As you turn it down, the source impedance is put in series with the volume control impedance (Ohm's Law) and the various construction foibles of the cable after the passive can then come into play. Generally this results in less bass impact and a sense of lacking dynamics. Due to the increased impedance the resulting sound is at the mercy of the interconnect cable.
Those successful with using passives will instantly know what I am talking about- as they have found that the choice of cable is pretty important!
For this reason it is better to have a low source impedance driving the cables. This reduces the effect of the cable as the source impedance is a shunt across the resistive/capacitive/inductive effects of the cable and thus reduces their influence. Now if your source has a good quality volume control then you are all set- but if it doesn't, you will need a good volume control to do the job and to do it right, one that is buffered from the interconnect cable such that the volume control's resistive value can't interact with the cable (and the input impedance of the amp).
Another solution is to have the volume control built into the power amplifier.
This is all just Ohm's Law so far.
Now if you happen to have more than one source you have a bit of a problem without a preamp. Some DACs solve the problem by having multiple analog inputs, but if you have been in this sport for any length of time you know how quickly digital technology is changing. So a preamp with a proper volume control and a low output impedance (so it can minimize the effects of your interconnect cable) can be a good investment and quite often one that reduces coloration rather than increasing it, on account of the reason's listed above, all having to do with Ohm's Law. Unlike human laws, Ohm's Law cannot be violated.
Historically the idea that the interconnect cables can be controlled comes from the recording industry and industrial electronics. It has only been in the world of home audio where higher impedances tend to be the name of the game that audible cable differences have cropped up (again, Ohm's Law) due to higher impedance impedances in amplifiers and often higher output impedances in source components. It should be no surprise that in such situations the addition of a passive control between the source and the amplifier will result in coloration. The way the recording industry got rid of such colorations (and BTW they often deal with very long interconnections so cable coloration can be a huge problem) is by operating with low impedances, often 1000 ohms or less (600 ohms was for a very long time a standard for line level connections; very few high end audio sources or preamps for that matter can drive 600 ohms although there are a few that can).
We all listen to LPs and CDs generated by this process; we thus all know that the recording industry's technique works. Its not an exclusive; the same technique works in the home as well.
