I've just fitted a pair of Akropovic pipes & Kev's O2 mod and can quite honestly say I'm pretty over the moon with the results.
They work really well together power delivery is much stronger , cleaner & smoother from lower rev's than before. No horrible shuddering low down now. I have got the fuel mod as well but not fitted yet I'm only thinking of fitting it later if I change the standard air filter to DNA. I did remove the snorkel up until it's first service then put it back in, mainly because I intend to ride a few dirt roads and found that after the last hose down water can get under the seat and lay in the bottom of the exposed filter. Which leads me back to the exhaust fitting. Akropovic supply a heat sheild replacement with the pipes that fixes in place where the mounting bracket go. But looking at it on the initial first fit it leaves big gaps in the rear under guard assembly which would allow water & mud to spray up from the rear wheel & find it way onto all the electrics behind the battery. So have used all the original parts instead which seal things of nicely. I'm thinking the most rearward heat guard has changed slightly on a 11/12 model as the photo instructions included show things a bit differently.
The noise level of the cans isn't much louder than standard but a nicer note, the decibel killer inserts are still in as I often find my self coming or going to work between 1am- 4am so keeps the Neighbours happy. I'll give them a go one day though without the inserts to see what they are like.
Just also say a big thanks to Kev for finishing off properly what Yamaha started great work mate, & hope your enjoying the new MT

Just given the bike a blast without the Db killer inserts in.
Motor pulls like a train. Fairly noisy under hard acceleration, cruising speed is fine, idle is quite loud and shakes the ground a bit. Also the whole bike felt more vibey through the rev range. And the AIS pipe DEFINATLY needs pluging in full fun mode unless your a fan of 21 gun salutes.
I'll be putting the inserts back in tomorrow.

When I had Akras fitted, I also found that the bike felt smoother and had a little more low down grunt with the baffles in.

If you find them too quiet with the baffles in, but too loud with them out, then a good compromise is to run a drill through each one of the holes in the baffle enlarging them slightly. This seemed to achieve the perfect balance between sound quality, performance and politeness for me.

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Funny you should say about drilling out the holes I was so close to doing that before reinstalling the baffles earlier today.
If I was only using the bike for weekends I'd probably leave them out, but for day to day use I prefer them in. Thanks for that something to consider down the track.
Did you drill every hole or a few?

Just re-read your comments Pleiades, you did re-drill all of them, Cheers.

I actually started by drilling every other hole, then ended up boring out all of them.

Looking back, I can't be sure it was 1.5mm; it was a while back and I don't have the exhaust anymore. Anyway, you get my drift - offer up various drill bits to check; start small and work up.

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Glad you are over the moon with your mods, adding a few bits really make these bikes run great.

I am enjoying the MT & have done many mods to it from full suspension to brakes upgrades & have a working O2 controller that really smooths out the MT's ride.

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Mods that I have done to my XTX's

My 04 XTX
Stage 1 & 2 DNA filters / Kev fuel mod / snorkel mod / Drilled air box mod / Engine breather mod / Fork Spacer mod / 15w fork oil /
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My 07 XTX
Raptor 700 cylinder 102mm / Modified Crank Case to take a 105mm Raptor Cylinder / 11:1 102mm JE Raptor piston / Stage 1 Raptor Hot Cam / Ported head / Colder Spark Plug / +2mm Throttle body / DNA stage 1 & 2 filters / Modified Air Box / Snorkel removed / Worry Brothers stage 2 filter cover / 6mm & 8mm Bolts Replaced with Titanium Bolts / Recovered seat in Black / O2 Eliminator /

My 09 XTX
59HP at the rear wheel / Stage 2 Raptor Hot Cam / DNA stage 3 Air Box / Carbon Can Exhausts / Modified Exhaust Link Pipes / PCIII With Custom Fuel Map / Wideband Commander O2 Data logger / LCD100 Dyno Jet display & fuel adjuster / 2500 OHM HT lead instead of a 10K OHM XT lead / Extra Coolant Cooler / Protaper Fat Bars / Tail Tidy With LED Tail Light / OKE Protection Knobs / LED indicators / AIS blocked / Modified rear sprocket rubbers / Rear Foot Pegs removed / 09 ECU With 02 Sensor Changed To A 06 ECU / Complete wiring harnes Changed from 09 to 04 / Home made LED resistor flasher / Hole drilled in the fuel tank filler neck to allow quicker filling / Modified Bar End Weights / Progressive front fork springs, 15W fork oil, forks lowered 25mm, used XTR rear links lowering the rear 20mm, rear spring one click stiffer / Changed front & rear guards from blue to black / 47T rear sprocket / Speedo Healer V4.0 / Kev throttle cam mod / Throttle grip mod / The new 2010 O2 sensor mod is out, works a treat, The new 2012 O2 Controller is out, PM me for details

Now ride a 2018 MT09SP ABS + TCS

My KTM 990 SMR Mod book. http://www.ktmsmt.com/viewtopic.php?f=13&t=4946

I found the best balance was just removing one of the baffles and leaving the other in.
I like the AIS bangs, a good way of making presence known in traffic lines and tunnels

Cool. There must be some tunnels around here somewhere. Otherwise I'll have to ride back to the UK visit the folks and go for a spin through the Dartford Tunnel !!