I think this what you want
Choose a blank Init Drum patch.
Edit
On the Osc/TunePage you have 2 options
If the Wav is in your keyboard press Name and then search for your Wav
If not in your keyboard press New Waveform and load from a USB

If I understand correctly, you want to play a full (or at least extensive) backing track.

Other practical options might be to have various backing tracks on an external device and "play them" either through th A/D inputs or USB.

Another option would be to have the track on your MODX as an Audio Song, which you can play (trigger) with transport control buttons.

I did this for a little while with audio Sound Effects stored on a Boss RC300 Looper. This way I could start/stop, and "bank up" with footpedals, and I could time backing track to what I was playing... and not time my playing to the backing (which was impossible to get right)... real drummer, no click track.

I have a wav file that I want to trigger by using a note (C1) to start the playback and combine that with a piano performance to start and switch to a violin performance at the end of song. Basically I am trying to make a performance for Baba O'Riely. I have an isolated wav track of the synth arpeggiator part that I want to have play through out the song and be able to play the piano part at the beginning and switch to violin for the solo at the end. The part I am stuck on is getting the wav file to play using C1 as a trigger. Hope this makes sense

Assigning the audio clip (.wav) to a Drum Kit Key will allow to have the audio play without having to hold the key down…

Select a PART containing a Drum Kit
Press [EDIT]
Activate the Drum Key “Keyboard Select” and select your target Key, C1
This will recall the data of this Key
Touch “Osc/Tune”
Tap the “New Waveform” box and load your .wav to C1
Set “Assign Mode” = Single
This will only allow one instance of the Waveform to play at a time — each time you touch the Key the audio will restart, replacing the previous.
Set “Rcv Note Off” = Off (Receive Note Off: is what allows drum/percussion sounds to play the complete envelope without you having to hold down the Key as you do with so called Normal instruments.
It will prevent the sound of the audio clip from ending when you lift your finger

Touch “Level/Pan”
Set your Amplitude Envelope
Attack Time = 0
Decay1 Time =127
Decay2 Time = 127 (maximum) Hold
Decay1 Level =127
This envelope will let the full audio clip to play without you holding down the key.

Finishing touches:
ALTERNATE GROUP. An Alternate Group (there are 127 of them per Drum Kit) allows any sound assigned to the group to cancel any other sound assigned the same group. You are probably familiar with this when working with hihat sounds. By assigning the Closed, Pedal and Open Hihat sounds to the same Alternate Group, playing one will stop the other from sounding. You may want to assign the KEY C1 to an Alternate Group… then assign another Key to that same Group to Stop the audio clip, if/when necessary.

thanks for the responses. will give it a try and see what happens