I have always been either, micing my amp or connecting to the amps' (or my attenuator's) line out, directly to my interface.
 
On the amp, the line out description says:
The LINE OUT 1/4” jack is for connecting to power amps or mixers. The LEVEL control adjusts the output to prevent overloading amp or mixer inputs. The CABINET VOICING switch will simulate the frequency response of a guitar cabinet, and prevent excessive bass or treble going to your mixer. This greatly aids in sound quality because you do not have to make extreme adjustments to your mixer EQ. The output level is more than adequate to drive any professional mixer or power amp.
 
I guess since it "works" without a DI box, I don't need one but will it sound "better" with one? I haven't used the cabinet voice option. I have been using cab/speaker IRs from within Sonar.
 
Thanks

A DI box (for guitar->mixer) has a high-impedance (500k or higher) jack input for guitars, often a jack output to then continue to your pedals and amp, and on the other side there is an XLR microphone level output to go to your mixer/interface microphone input.
 
If you use this type of DI box, you can play your guitar with your pedals running and your amp feeding back, but what you get on your recording is just your clean, direct guitar signal.
 
This allows you to "re-amp" your guitar afterwards. So in other words, it could be that as your song develops, you decide a crunchy distortion would have been better than a metal distortion. If you recorded clean, you can do this.
 
Amplifiers often have  line outs, as yours has. If your interface has a 1/4" jack input, then you do not need a DI box (unless you want to record the signal before any pedals you might have).
 
Your output has a cabinet simulator, but it is not clear whether the output is pre-preamp or post-preamp (typical guitar preamps have 2 channels - clean and distorted). This will also come into the decision you have to make.
 
Bottom line: If you have a jack in on your interface, no, you do not need a DI box.

Thank you!

What you have to be careful with is the input impedance of any 1/4" jack input. Not all jack inputs are designed to connect guitars direct to them at all unless they are labeled DI input.
 
For example a jack input might have a 10K input impedance and that is not so suitable for connecting guitars direct to. What will happen is the signal will work OK but you might find the very top end of the guitar sound will disappear. The jack inputs on my Yamaha digital mixer for example are 3K input impedance which is way too low for a guitar. It works fine but the top end really gets shaved off.
 
Check the specs of your interface and look up and see what any jack input impedances actually are. It will be in the specifications.
 
A DI box usually offers quite a high input impedance to the guitar in order to preserve all the signal level and frequency response. It is actually a great way to record guitar because it not only presents the right impedance to the guitar but it also connects to the Mic XLR input usually where there is also much more gain available for guitars with passive pickups etc..
 
A great way to record guitar also is to plug the guitar direct to the DI box first and record the clean dry signal from the XLR output. Use the jack output from the Di to feed pedals, effects and amps etc and also track that guitar from there. You might need two or more tracks to record the guitar part but having that super clean dry guitar signal available later on will come into its own once you start applying amp sims and processing etc over that dry sound.
 
 

+1 what Jeff said. On my interface, the Line Inputs (9-16) are 10K ohms. Line Ins 9 & 10 are switchable to Direct Instrument Input with <= 1M ohms input impedance. Here's how that changes the level specs (same gain for very different input level ranges):
 
INST IN (IN 9-10) Connector 6.3mm (1/4") TS-jack (T:HOT, S:GND), UNBALANCED
(When set to "INST" at LINE/INST switch)
Input impedance 1M ohms or more
Nominal input level
GAIN: MAX -57dBV (0.0014Vrms)
GAIN: MIN -12dBV (0.251Vrms)
Maximum input level +8dBV (0.2512Vrms)
Gain 45dB
 
LINE IN (IN 9-10) Connector 6.3mm (1/4") TRS-jack (T:HOT, R:COLD, S:GND), BALANCED
(When set to "LINE" at LINE/INST switch)
Input impedance 10k ohms
Nominal input level
GAIN: MAX -41dBu (0.0069Vrms)
GAIN: MIN +4dBu (1.228Vrms)
Maximum input level +24dBu (12.182Vrms)
Gain 45dB
 
Edit: My bass amp (a v3 Fender Rumble 200) has a DI output, but the signal quality level is nothing like it would be from a Radial JDI Passive DI box with its Jensen transformer. I bought that amp for its flexibility. It has an effects loop in addition to the DI output, so pedals can be inserted post-DI, pre-amplifier and its on-board effects. I use a Sennheiser e 609 to mic the amp, so that gives me both dry/clean and wet signals. I can get better audio quality with discrete boxes, but what I have is WAY better than my current playing ability, so it's up to me to woodshed enough to justify the additional expense (that Radial box ain't cheap).
 
Edit 2: FWIW: http://www.radialeng.com/jdi.php

The specs of the Profire instrument input is:
 

Inst. Inputs (Unbalanced) At Min Gain, No Pad

Frequency Response: +/- 0.2dB, 20Hz to 22kHz

Signal-to-Noise Ratio (min gain, no pad): 107dB (A-weighted)

Dynamic Range (min gain, no pad): 107dB (A-weighted)

THD+N (min gain, no pad): 0.0025% (-92dB), 1kHz, -1dBFS

Crosstalk: < -110dB @ 1kHz

Maximum Input level: from +14.5dBV @ min gain, no pad to -39dBV @ maxgain, no pad

Input Impedance: 1M Ohm unbalanced

Adjustable Gain: >53dB without padInput impedance is 1M Ohm. That is what I plug into when I use amp sims or when I have connected my amp's, or attenuator's, line out to.

Jeff Evans
 
A great way to record guitar also is to plug the guitar direct to the DI box first and record the clean dry signal from the XLR output. Use the jack output from the Di to feed pedals, effects and amps etc and also track that guitar from there. You might need two or more tracks to record the guitar part but having that super clean dry guitar signal available later on will come into its own once you start applying amp sims and processing etc over that dry sound.

 
+1
 

You should be fine with what you are doing - you don't need a DI. Line out to line in. You are using the amplifier's preamp to get to line level. What would be better? If you are using a microphone a mic preamp is a good choice, if you're using a guitar a guitar preamp is a good choice. I have a number of different ways to interface my guitar to my computer, but for using amp modelers or effects I prefer using a guitar preamp. I have a guitar amp with an effects loop and I can switch my interface in and out of the loop. I also have a separate guitar preamp I occasionally use. A guitar preamp is designed for guitars and has the feel and response that most guitarists like. Micing an amp is nice, but it's problematic in a home studio. My 2 cents. 

Just remember that if you are passing your guitar through any pre-amps etc before recording that sound will always have the sound of that pre-amp included in the recording.
 
I have found from experience that if you are going to start modifying that guitar sound with amp sims and processing etc the best result comes from having the total raw guitar sound direct from the guitar itself as pure as it can be and the only way to get that is from a DI connected direct to the guitar itself. Nothing between guitar and the track you are laying down.
 
The trick is to use more than one track to track the guitar. One super clean track as above plus another that is either miked or recorded direct from a later stage in the preamps etc. Then you have got more options. I sometimes track guitars onto three tracks. One super clean, one half way along eg from some output along the way and the speaker miked up for good measure. Then you have all the options available to you.

Thank you for the good information! I don't have DI box (yet) but I have been looking at them on and off.
 
I generally do not like amp sims but playing my real amp and then applying an amp sim later might do the trick. I don't mind the way amp sims sound afterward. I just don't like hearing them while I am playing.
 
Do you have any DI recommendations as far as brands? Passive vs active?
 
Thanks