This is a difficult question you have posed. Here are some suggestions for you to check out:
1) A group called The Mavericks, who had their best days in the 90s. They were never big stars. I think they have much more of a "rock" sensibility than most country acts. Interestingly their music has Latin influences as well, as their lead singer is a Cuban-American from Miami, Florida.
2) Any one of many individual country songs by many different artists where the session lead guitarist was Kenny Greenberg. He also recorded on a lot of contemporary Christian records -- you might not like those as much, and they don't rock as hard either.
3) There was a genre in the 1980s called "cowpunk" which combined country music sensibilities with the instruments and (very loud) sounds of stripped-down hard rock. The quintessential band in this genre is Jason & the Scorchers. The Georgia Satellites are also worth checking out.
4) In the 1970s there was a movement called Southern Rock, in which bands combined country influences with rock, and often indulged in long lead-guitar-heavy instrumental improvisations. Most modern country music fans love Southern Rock. Bands in this movement include Lynyrd Skynyrd, Outlaws, The Marshall Tucker Band, and Blackfoot. You should certainly check out The Allman Brothers Band, who came to prominence in the late 1960s before the Southern Rock movement, and combine country, blues, rock and psychedelia.
5) Several country music singer-songwriter-bandleaders who had their greatest days in the 1960s and 1970s are revered by American and British rock musicians today. These include: Willie Nelson, Waylon Jennings, Johnny Cash, Merle Haggard, Buck Owens, Kris Kristofferson.
6) In the last decade, hard rock guitarist Jack White (who recently performed with Robert Plant of Led Zeppelin) has produced albums for several traditional country artists from the 1950s and 1960s who are now quite elderly. These albums are very traditional, but perhaps you can hear what it is that Jack White admired in these artists and their styles. He has produced albums for Loretta Lynn, Wanda Jackson, and Jerry Lee Lewis. He was also associated with the late Porter Wagoner in his comeback tour shortly before his death.