Is there any reason i can't connect a headphone output (of a external sound card) to a hi-z guitar input (8 track recorder)?

Is "line - in" a better option?

The reason i ask is my sound lacks clarity and i'm finding it hard to make it clean. Before i waste time diagnosing the issue i wanted to make sure i had the fundamentals in place.

What exactly are you attempting to do?

Your hi-z and line-in will have different impedances, and your headphone output is stereo TRS whereas your inputs are both TS, most likely, meaning you will be getting unpleasant sounds no matter what.

If I know your intentions, I might be able to help.

I have and external sound card for my computer with a hi-z guitar input in which a plug the guitar. It has a line-out which goes to a stereo system for the general computer audio, and it has a headphone output. It is this output which i have connected to a hi-z input of a digital 8 track recorder (boss br 600) with built in effects etc.

Today i thought i'd use it make a 12 bar blues backing track. I launched Guitar Rig and selected basic clean zero gain amp setting and tried some preset clean set-ups.

The sound i heard from the 8 - track was thick and buzzy with no clarity compared my headphones plugged dirrectly into the sound card.
Well I'm guessing since the soundcard/interface has a guitar-in, it's a pro-audio line level device. If you're trying to go to the recorder, you should use the line out from the interface and go to the line-in on the 8 track. Also check the gain on the recorder and make sure you're not recording too hot and clipping the sound.

However, I guess there is a chance that your soundcard is consumer line level which won't match with the 8 track, meaning ugly sound. Does Guitar Rig not have the option to record? I'm not familiar. You can always record guitar direct into the 8 track. Also, check to see if your guitar amp has a direct out (if you have an amp). That can be plugged into the 8 track.

Long story short, your line-out should be better than the headphone out.
The gain on the recorder, that's the problem, thanks for the advise. I should have noticed the little red light flashing as i played.