This is a midi related issue -- sounds like it anyway. If you are using an older version of acid #1) it does not have midi suport and #2) wav file recording in acid totally sucks, you will never be able to get a hot enough signal. if you do it will be noisy as hell. ACID really sucks at recording. If you have ACID 3.0 read (read on even if you do not)
I would not do it this way. ACID 3.0's midi capabilities blow (yes even for syncing). If you want to sync up your 880 w/ acid and you are using ACID as the slave you should make sure that the beginning of the acid tune does not start for a few measures so each unit can play catch up with each other.
You are better off creating what you want to create in acid, then convert it to a wav file and record the wav into the digital in L on Track 1 and digital L on Track 2. Walla, you have a stereo track. I used to do this all of the time because I use ACID to create my beats (one shots)....then lay down your tracks on the 880.
--What about this------> save your ACID project as 4 different .wav files
Wav 1 = drums and percussion
Wav 2 = synths and whatever
Wav 3 = fx
Wav 4 = basses
How?
1.) create your ACID Project.
2.) mute everything except the drums.
3.) Save that as a wav (titled something like this - "project1drums"
4.) mute everything except the synths.
5.) save that track as a wav (titled something like this-
"project1synths")
repeat as needed
6.) Now import your 4 wav files into Cakewalk/Cubase/N-tracks or whatever program you are using. (they will all be in time with each other. How? Its magic -- all wav's were created in acid. they will all have the exact start and finish times) - trust me they will..
7.) Now you can either tweak these tracks in the editor (Cakewalk, cubase.....) and record directly into your editor
Optional
8.) You have the option of bouncing these 4 tracks to 1 track after your tweaks.
9.) record the wav files into your 880.
10.) lay down your other tracks
Digital and midi are two different beasts.
I hope this helps
Bill