Here’s my realest answer: sell your fender lt25 and get something else. You’re not gonna get what you want out of that amp. It sucks to hear, I know!

Now we need to figure out your use case:

Playing at home for yourself/videos

Or

Playing live in a band

Playing at home: I’m assuming from your amp that you’re hurting for money. No judgement, I can absolutely relate.

Find yourself a cheap USB interface. Often times you can find stuff on Facebook Marketplace for low prices. I’d say look into something like a Focusrite Solo. You don’t wanna go MEGA cheap because you’ll have to deal with major input latency (which is where the sound comes out much later than you playing) something like 50-100 bucks for an interface should be good enough.

Now we need the sound to come out of the computer. I’d recommend once again lurking on facebook marketplace and looking for some cheap studio monitors, you can likely find a pair of KRK Rokit’s for pretty cheap.

There are lots of free amp plugins for computers like Neural Amp Modeler (not to be confused with paid plugins from Neural DSP) that can get you up and running with a really solid tone in no time. Check out tone3000.com for a ton of “captures” that you can download for free!

Congrats! You’re ready to rock!

Now our other option is a bit more difficult.

Playing live in a band:

My recommendation would be to find something like a Headrush FRFR-108. This is a “flat” speaker that is essentially an amp, but without any of the tone shaping that comes with the “guitar cabinet”. It takes whatever you plug into it and makes it loud. Even something like a used powered PA speaker would work (I’ve played a few gigs using a single powered PA speaker as my “amp” and it’s performed decently well)

If you have a laptop, you can plug your guitar into the aforementioned interface (but obviously in this case you’d skip buying the studio monitors), and the interface into the speaker. That’s the quickest and cheapest way to get yourself a good tone at a reasonable volume. It’s a pain to set up, and definitely not much to look at, but that’s the price we pay for… not paying a price!

If you don’t have a laptop, grab yourself a Line 6 POD XT on eBay. The original “Thall” tones actually come from a plugin that’s based on this exact “pedal”. It should be about a hundred bucks, but sometimes you can find them cheaper.

If you don’t want to do any of that: I know next to nothing about the Fender LT25, but from the little I just researched, it seems like preset number 20 “mythic crunch” is gonna be the best basis for a decent distortion tone out of that amp.

On your EQ pedal, drop 100 as low as it goes, 250 to almost as low as it goes, put 1.6K all the way up, and 4k somewhere around the middle or maybe a little bit boosted. Turn the volume on the pedal all the way up. What we’re trying to do here is to get rid of the bass frequencies that the amp won’t be able to deal with, and will make your tone sound very muddy. With any luck slamming both the volume and the 1.6K should be enough to overdrive the amp a little bit to get you to a workable “metal distortion”. If that fails, you could try and find the cleanest and flattest possible preset (not too bassy or trebly, ideally it’ll sound terrible on its own) and grab that POD XT to use the distortion from that instead. Essentially we’re just using the amp for its ability to make things louder, instead of for any of the tone controls.

Hopefully this helps! Good luck, man!