Alright, I took the plunge. I'm trying out a UA Solo 610 tube preamp. So far I have only been trying it out as a bass DI, and I'm not that impressed, so I'm looking for some advice. I've been playing with it for hours, but there's a good chance the problem is user error, so feel free to point me in a better direction. Here's what I've been doing to A/B it with the built in DI in my board: 1. Rickenbacker 4003 into the 610, 610 output to a channel on my Mackie Onyx 1640. Mackie channel gain varies depending on how much signal I'm putting out from the 610 at the time. The meters on the mackie hover in the green/yellow range and occasionally hit the red very briefly, depending on how much 610 level there is (and I can only turn the mackie gain down so much). 2. At the same time, I take a bypass signal out from the 610 into a second channel on the Mackie that allows direct input for guitars/basses, etc. Channel gain remains constant, since the bypass signal is always the same level. The meters on the mackie hover in the green-yellow range. So presumably I'm getting one channel coloured by the 610 primarily (with a little bit of Mackie influence) and one channel is pure Mackie. The performance on the two channels is identical. I play for a while, I adjust the 610 gain and level controls everywhere from way down to say 9 oclock maximum, first one, then the other, then both. I have to adjust the gain on the mackie as I go along so that the channel that is taking the signal from the 610 doesn't clip much of course, but other than that I'm not changing anything. Then I listen to the two tracks in my DAW, switching back and forth after setting their levels so they're equally loud on playback. After all that, I can hear a difference, but it is a very, very small difference. The 610 channel is slightly warmer, and I mean very slightly. No matter how much gain/level I push through the 610, the difference between the two tracks is so subtle that either (a) my ears suck, (b) I'm doing something wrong, or (c) the built in DI functionality on the Mackie is actually very good. Or (d) none of the above. By the time I get enough gain from the 610 to cause some distortion and make a real difference between the two channels, the Mackie meters are pinned in the red and the gain on the mackie is as far down as it can go on that channel. Although strangely, even when the mackie says it's clipping, the signal in my DAW is nowhere near clipping, and I don't hear clipping on playback (and I have turned up the mackie firewire output level control to close to maximum - but that's a separate problem, maybe). Anyone have any ideas what's up here?