ART Tube MP Original Tube Mic Preamp ......

Norrie,

they are OK and worth having.  They can sound good on the bass, in a wooly kind of way.  They are solid state but run a tube (value to you guys across the channel) at low voltage - mostly as a marketing thing but you can get some hair on a sound.  Otherwise, it is just a preamp like you'll find in any interface.  I forget what the gain is, but there is an in and out, but that runs through the tube so it isn't as useful as on a Gap Pre - or Neve (w/o saying).

It is a great live tool as well as useful in the studio.  It is a DI, and outputs both a balanced XLR and 1/4 inch line, so you can put it in the tracking room, DI and send a balanced signal to the control room.  Live, you can plug it in and send one signal to the snake and the other back to an amplifier.  It is a nice little tool box, just don't let anyone tell you it is a real " tube"  piece of equipment.  You get what you pay for.

Two caveats - some are noisy.  Check them.  They will all be noisy if you crank them, but from what I've heard some are almost too noisy to use.  The other thing is price.  You can get them for dirt cheap at times here in the states.  I bought mine for $50 and that was 6-7 years ago.  I've seen them for $35, I think.  Make an offer for two of them, and check them before you leave for noise.  It is a pretty good deal for a nice tool.  Not a great studio preamp but a good tool to have around.

@

They aren't bad but they aren't anything to write home about. I had one and it crapped out after a year or 2. I haven't bothered replacing it if that says anything.

If you replace the cheap 12AX7 Chinese junk tube with a New Old Stock tube or one of a lower mu (gain) you can get some better sounds. A 7025 is practically the same thing as a 12AX7 but has a lower noise rating. If you can get a N.O.S. JAN (Joint Army Navy) one those usually resolve some of the noise issues and sound much better. I think a lot of the noise is just down to the value/tube.

The VS-700/Octacapture pre's are better IMHO.

I'd just take the DI out and go into one of the 1-8 analog in's on the VS700. Either via XLR to XLR or XLR to TRS. Depending if the DI needs phantom.

Does the bass player really want the sound of the amp? Otherwise I would just take a DI off the bass first. Once that's into SONAR you can make any edits (if need be) and then just re-amp it with something like this if you want passive, this if you want active, and if you have a fancy API 500 box :) then this.

It looks like the EBS 350 just has a line out. You should be good to go taking that out into the VS-700. Be cautious of ground loops/buzz.

I'd throw a Mic on the cab just in case. You may not use it but I've found sometimes it's better to have something extra later on when mixing, unless you're running out of ins.

Norrie,

the Art tube preamp has both a line and balanced out.  You can use the balanced output to run to the control room.  Take the line out to the bass amp.  Two for one - which is what I meant about it being a good tool.

As to the sound - it is alright if you use a low output.  But the higher you do input and output the more of the low voltage tube sound you get.  A little and you get a rounded tone.  More, and it doesn't get prettier.  It is a fairly versatile preamp, esp. for the money.  There was a shoot out between it and the Great River at Gearslutz and a lot of people picked it for bass.  Just goes to show you.  I've used mine mostly for live, but also in the studio.  It sounds good enough as long as you don't get carried away with driving the tube (which can sound good live).  Otherwise, you can make it can sound big and round.  It wouldn't be my first choice (I like the Portico II much better - cleaner and sharper), but it works fine if you need another preamp/DI.

@

I have had 2 of them since 199?? .  They are basically a DI box and that's what I use them for. What makes them a little different is they have XLR inputs as well as the 1/4". That's something I've never seen on any other DI box. So I guess they designed it to be a pour mans mike pre amp as well. I've never used it much on a mike as I can't really hear that there is an improvement of any kind. They don't really add the warmth factor as far as I can tell. Just because it's tube don't mean it's "great" tube circuitry. But they are handy and for that price they are excellent DI boxes. I had a hum problem at first and the tech at Art told me to clip the ground pin off the power supply. Worked.
I put Groove Tubes in mine when I got them. Never had to change them.
They are great for beefing up wimpy acoustic instruments. This is what I find most helpful. A lot of acoustic instruments either have weak or no pre amp. So I always have them on the stage ready to go.
Super fast to set up a nice hot level using the on board peak light.  The pad system is very easy to use. 
For Bass they work great in the studio if you want the direct PU sound but you can also put it in line with any DI output.
I also found them useful to add phantom power in certain situations where I did not want it on that group from the FOH mixer.
As a serious mike pre amp, no 20% 
As a Swiss army knife DI yes 100%