Ever perform a preamp bypass comparision test?

I have a quicksilver line stage that I have done a simple mod on- I have taken the leads from the tape in jacks and unsoldered them from the tape switch and soldered them in parallel with the output of the attenuator, so I have both an active on one output and a passive on the other, all using the same exact switches and attenuator.
I have never seen much sense to a preamp being an improvement, after all, all we really need one for is to switch between sources and volume control. Why pay big money for something that is suppossed to do as nothing as possible, why not do nothing in the first place?
There is another side to the argument that says a matching devise of some sort is nessessary for the best sound evan though a passive may work. while of corse we all know this is system dependant, and obvious because different components have different input and output qualities, there seems to me to be much more to this, and I find it intreguing.
Needless to say, I find the passive more transparent, (but realize that the quicksilver is not supposed to be the most absolutely transparent preamp possible). The passive does not seem to always go as deep in the bass as the active does, and while it may seem that the extra depth that the active does is due to either the effect of gain, or the fact it is tubes, I'm not convinced that it is artificial. The deepness that I am referring to is not just more bass that is always present, but rather deep bass that it seems is suppossed to be there when the program calls for it.
And also, I find that sources that are suppossed to be good for driving a passive and not good for for a passive (due to the output impedences) don't seem to be following the rules. My theta cd player seems to benifit more, or suffer less from a passive, while my micheal yee phono amp which has the lowest gain of all my sources, seems to benifit the most going passive.
Also, amps that I have tried this with that I would think would benifit from an active stage due to thier input impedences sound better with the passive, both a pse studio IV (50 ohms) and a hafler dh-200 (33 ohms). No loss of high frequencies at all. This seems to be true no matter how much I have to crank up the volume to drive them.
These have all been with only 1 meter interconnects, and I have yet to try long ones, and I plan on trying more amps. All of my comments have been thinking only of transparency, or what I am believing to be accuracy to the signal, but I am not really sure if while at the same time I am losing information and details going passive, that the active is not the most accurate to what the signal is intended to be. The quicksilver is neutral, I can say that, and right now I am enjoying the option of going either way. I'm on the fence.

We're still on slightly different pages here Sean, so maybe it is me who's not being clear. What I am suggesting is to stay with one set of outputs from the DAC (could be either one - the variable ones could be useful for achieving an overall volume that doesn't blast away the subtle differences, but once it's set, leave it there and treat it as fixed), or to use any other source. The idea is to focus on what *the preamp* is doing to any line-level signal it gets. To do this, you have to maintain the same interconnects and I/O jacks, and just swap the output leads on the preamp from the active, normal ones to passive, direct ones like processor bypass. That way, you can compare the sound with and without the effects of the preamp's gain and attenuation stages, while keeping the connections and cables constant. To do this, you must set the volume control on the preamp to unity gain, wherever that may be. What you are describing is comparing the sound of your DAC's attenuation to that of your preamp's, which is a different comparision, and one that only matters for that particular source component (it does tend to confirm that your preamp must have a quite transparent gain stage and jack complement, as well as your interconnects being very fine, since you're losing one set when you go to the DAC's internal volume control, and as we theorized above, it could mean that the two attenuators behave very similarly, but your test does not isolate the preamp or maintain all the other variables as constants - it's a legitimate and useful test, but a different test nonetheless).

Basement, I'm not completely sure about this, but I think most preamps place the volume attentuator after a gain stage, so it might be that taking an output straight from the attenuator bypasses the output stage, but is not totally passive. The loss of bass when you run in this mode could very well be due to the interaction of the volume pot's output impedance with the load presented to it by the amp and interconnects when the normal output impedance-lowering buffer stage is not present.

I'm a little confused by your fifth paragraph, but maybe you put 'passive' in some spots where you meant to write 'active' (also, your phonostage is actually going to possess the highest voltage gain of any of your source components, although not probably the highest output voltage). In the next paragraph, I'm sure the input impedances you refer to on your amps must be K-ohms, not ohms, but again, it would be bass frequencies which would be rolled off if the input impedances were too low, not the highs (it's cable capacitance which can roll off the highs.) Help me out here Sean if I've screwed up any of this!

Drubin, what I've noticed in my tests is more of a subtraction from the sound than an adding to it, which I guess is good sign in theory. For instance, piano can lose a little of its sparkle and percussive incisiveness, rendering it just a little veiled in comparsion. Stand-up bass loses some heft and definition, becoming less pitch-precise and more rubbery. On the other hand, some sounds do seem to gain unwanted artifacts; a half-opened hi-hat cymbal sounds more like two pieces of metal clashing against one another when listening to the DAC straight, but when the preamp is inserted, the sound becomes more akin to indiscriminate white noise - could this be the result of added intermodulation?

That's my SS preamp, though; with my tube preamp, there are losses to be sure, but you do notice right away a certain subtle tonal quality (which I like to characterize as 'sunny') is lent to the whole presentation. It can be attractive once you get used to it, but that is certainly something which is added, probably low-order harmonic distortion, and I don't know how it can be considered to make the result sound 'more like music'. This preamp definitely sounded more like music than my older cheap SS preamp that departed long ago, which was grainy, shrill, and flat in comparision, but it doesn't IMO improve on the straight feed from a quality DAC.

Zaikesman, I was thinking of my own personal dilemma with my two preamps. The (active but no gain) Placette, which is very, very close to adding or subtracting nothing at all, and the First Sound, which can sound glorious and more musically convincing in some respects, yet sounds entirely different from the Placette.