Guitarist likes the sound he gets out of his amp - so I looked for a line out to go into my presonus which then goes into Sonar 8.5
There is a "speaker out" but when I use this I don;t seem to be able to change the recording level.  I guess I could always mike the amp - but would rather go straight into the board.  Am I missing something?
Thanks
 

Indeed you are!!
 
Speaker outs can hit several VOLTS in amplitude, not the millivolt levels which most interfaces expect to see.
You could have already completely fried your inputs if you've done this.
 
Second point, you cange the input level BEFORE anything hits Sonar. You cannot alter this post AD conversion so it needs to be done either at source or via your pre-amp/interface
 
Lastly, mike up the damn amp!! Any sort of line out or emulation will not capture the whole of the guitar tone thqat your guitarist likes - half of the sound is from the speaker/room combination. Developers are getting better & better at emulation, but it's still a fair way off yet.
 
 

Get a direct box that will allow you to take signal straight from the guitar and send it to your presonus interface.

BJ may have a point that you may have damaged you interface input. If you haven't, consider yourself lucky and stop that practice. The output of a guitar amp is made for one thing: a speaker. It's more complicated than that, ( it's kind of a golden rule to follow in the studio and live sound) and this is a very simple explanation of what not to do.

If it's a tube amp it needs to have a speaker plugged into it, or a substitute load (just a high-powered resistor). Devices are made just for this purpose, which provide the necessary load to the amp as well as a transformer-protected output for recording. But they're gonna set you back a hundred bucks or more. (I've heard of a DIY kit for like sixty bucks but don't recall its name.)
 
I'd just put up an SM57 or similar microphone and try it that way first, like Bristol_Jonesey suggested. It's certainly a lot easier! Plus don't forget that the amp is only part of the sound. Without the speaker it'll likely sound quite a bit different than what your guitarist is used to hearing.

Grem  A DI box is only needed to change the impedance of the signal and mostly this is only needed when working on stage to send a dry signal to the FOH,  Acoustic guitar or bass, most all sound people mike an amp.
There is absolutely no need for a DI box in a studio where your sitting 5'-12'  from your interface. 
You simply plug in directly using the interfaces instrument jacks. 
 
There is no substitute for a good guitar, a good amp and miking the amp. The speaker is a big part of the sound. Amp sims are OK for people who are after a processed tone.
Most of us are used to the response and tone we get when using a good , usually tube, amp. You will play better. 
The line out on most guitar amps is often not even after the pre amp so totally pointless. 
But there are many who like the processed type sound so there's a case for that person using a pedal board and /or going directly into the interface line or instrument  jack. 
 
That was real dumb to use a speaker jack, your bloody lucky your interface is still alive! Please take the time to learn the basics of audio before you touch any more wires....

Nah, Cactus, "dumb" is when you decide to take a voltage reading across a speaker, holding the test leads in place between fingers and thumbs -- on a vintage Twin Reverb where the transformer is mounted on the speaker assembly itself and the speaker connectors go straight back to the 6L6 plates. Once you regain consciousness on the other side of the room, you figure out that it's about 600 volts. By "you", I mean "me".

Cactus, you are correct in you referencing some of the different uses of a DI. But they are often used in recording studios when even a few feet from recording console.

Example:
http://www.tech21nyc.com/..ucts/sansamp/index.html

Many recordings you have heard used a similar device. To say a DI box is not need isn't really justified.

As a guitar player what I would like, if recording through an amp with no line out, is to get a direct signal to the recording board/mixer/interface.

Those are not DI boxes that I'm talking about those are modeling devices that replace an amplifier. So I see your confusion. That is what I'm referring to when I say pedal board.  
 
 

Not confused. There are other DI boxes as I'm sure you know.

Have a good day.

Wow - I think I lucked out.  I think my presonus interface between the amp and cakewalk seems like it is still OK - it made it thru that recording anyway.  I better go back and test it. 
 
Thanks for the input all - appreciate it.  Next time I will ask BEFORE I try something like this ! ! !