You can install a shallow 6" can made for 2x6 construction. Halo H27ICAT is the 6" you can use. Lots of manufacturers make these shallow cans.
You can use regular incandescent, fluorescent and LED lamps and have a large selection of trims. The only drawback is you can't use taller lamps or they might stick out the bottom. The most common is the 50PAR30 / 75R30 style lamps. These are also made in remodel style in case the ceiling is already up.
Here is the spec sheet for the H27
EDIT
I'll give this another try. I originally deleted this answer because it is not a slope can. Where I work, some people use regular can lights and use adjustable trims. Because of the depth you have, 8 inches, this can is 5-1/2 inches. I suggest you use a gimbal ring trim. It works like a eyeball, but the lamp is recessed so you don't get that 'bug eye' some people associate with eyeball trims. You can get the above can in 5 inch or 6 inch round cans, both IC rated, depending on the manufacturer your supplier uses. Think about a trim like this.
Make sure you use the same manufacturer as the can and trim to cover yourself. This gives you 2-1/2 inches for your channel and insulation. If this doesn't float your boat try going to a local lighting showroom and look at what they might have. If you want recessed you will find what you want. Consider LEDs to keep from getting the ladder out if your slope gives you a tall ceiling. While considerably more, doing it all together will be less painful. Either way PAR30 Halogen or PAR30 LEDs offer different beam spreads, so you can at least do something with the lighting.The biggest problem is you can't shine the light back to the wall, mostly straight down or with the angle the can is hung, not backwards. If you choose this, don't forget the dimmers!
Best Answer
Generally speaking, a room with a light-colored ceiling will appear taller than a room with a dark-colored ceiling. However, in a really small space painted in a darker color, painting the ceiling the same color will make the border between wall and ceiling disappear, making it more difficult to gauge the ceiling height by sight.
A related technique for rooms painted in "warm" tones is to tint your ceiling paint two shades lighter than your walls, but in the same basic hue. This will blur the line without creating a "closed-in" feel that a darker ceiling can create.
Using vertical stripes on the walls will draw the eye up and down and will make the walls appear taller than they really are.
You can also cheat perspective a little by blurring the line between wall and ceiling. Painting a gradient between the wall color and ceiling color, that begins on the wall and ends on the ceiling, will give a somewhat forced perspective that makes the room look taller. Similarly but easier, painting a border the same color as the dark walls on the white ceiling will give an impression that the wall continues slightly higher than it really does before the ceiling begins.
One last thing; while the recessed lighting stays out of people's way, it won't illuminate the full 180* sweep from the edge on one side of the ceiling to the opposite edge; you'll get a band of shadow caused by the angle that the light is recessed into its can or tray. This can bring down the perceived height of the walls. Try filling the room with light from other sources, like wall sconces or table/floor lamps, to put light up along the walls filling the shadow.