The inverted re-entry from Mars is quite possible - I've done it coming back from Titan even but that one is tricky. It's best to practice a lunar return until you get the hang of it before trying to do it from farther away.
The first trick is to get your Pe in the correct place (and on the correct vector). The PeA is very particular, and varies according to your entry velocity. Too low and you burn up, too high and you can't stay in the atmosphere. For a Mars return, I set my PeA at 68k, with a margin of 0.1 km. The Pe location is more forgiving - as long as you err on the saide of "farther" from base, not nearer. The direction also has some flexibility, the XR has good crossrange.
I don't use the Approach programs, they aren't accurate enough to get the PeA exact enough. I suppose you could start with Approach, then fine tune the PeA - but I use Delta-V for all my MCC and approach burns. Remember, Approach doesn't work with Map's Plan mode - only the course programs do - and you need Map's accuracy to perform a direct re-entry from Mars (or farther). Using Delta-V this way is a bit advanced, but not that difficult once you get the hang of it. I'll outline my method for a Mars-Canaveral trip.
Starting from the Mars surface: Open IMFD in both MFD's, and link them. Set the "landing Target" in IMFD's configuration page (this is needed to ensure the correct vector so you will pass over the base). Set up Target Intercept like normal (I suggest using the process given in IMFD Full Manual/Playbacks). Use Surface launch to get into the parking orbit, and Orbit Eject to make the transfer burn - just like you normally do. Once the transfer burn is complete, you are done with Target Intercept.
About halfway back to Earth start planning the first MCC. We actually start planning the approach here (while it's "cheap"). We want about a third of an orbit for the braking - more is OK. Cape Canaveral is about 89 degrees West, so we will just round that up to 90 degrees to simplify the math. We will add 120 degrees to that, giving us about 150 degrees EAST longitude.
Open Delta-V, and set the TEj large enough to give you time to plan the burn - say around 600s which gives us 10 minutes. Less, actually, we want about three minutes left on the clock (to allow Autoburn to orient the vessel for the burn) when we engage AB. Make sure Map is on plan mode (course shown in blue, not green). Hit Map's PG button until the it displays the longitude and latitude of the Earth periapsis. Then we adjust dVf until the longitude of the Pe is at 150E.
IMPORTANT: Delta-V needs at least 30s TEj remaining or it won't perfom the calculations, if time runs low just raise the TEj a few minutes. Also, Delta-V starts with a dVf of 10ms, be sure you set that to zero before trying to make adjustments.
Now start making small adjustments to dVi to adjust the PeA. This will also affect the Pe Longitude, so make small adjustments - and alternate adjusting dVf and dVi until both the longitude and altitude of the Pe are on target (doesn't need to be exact yet, just get in the ballpark).
Now change the PG on Map until it shows the landing base's name and an Ang value. We want the Ang to be zero, so we adjust the dVp to alter it. Again, ajusting the dVp will affect the Pe location and altitude, so there is a lot of "back and forth" using small adjustments (and lot's of changing Map pages, etc) until the Pe longitude and altitude are close to the target values, and the Ang is close to zero. Again, it won't be exact yet, just get it in the ballpark. Once we get these values adjusted, we sill look at the Periapsis' Latitude (we've ignored that up until now). It's not that uncommon, especially coming from Mars, that we are approaching on a close to (north) polar insertion. If the Pe's latitude and inclination are high (much over 70 degrees) it can be a problem - we will have much less "distance to base" than we need, and will need to readjust our course to come in over the South Pole instead.
Once satisfied, engage Delta-V's AB.
Once we've covered half the remaining distance, make another MCC using the same method as above. We'll do this a few times, each time we cover half the remaining distance. With each MCC, we increase the accuracy of the desired course. Our last MCC/Approach burn will actually be made well outside the Earth's SOI.
Re-entry: Dump remaining main fuel. More mass means more inertia, which means more inverted lift will be required to prevent skipping out of the atmo - too much mass and you won't be able to stay within the atmosphere. Set the XR's Attitude AP to AoA=80, Bank=180. We don't want any inverted lift yet, as that would lower our PeA and cause Flaming Death. When we reach the Pe, we need to lower the AoA. This is the trickiest part of the entire flight. We need to find the correct AoA VERY quickly. We want a VS and a VCC of Zero (or as close as we can come to zero). This will typically be around 30 degrees, so I remember how many times I need to press the "8" key to get to 30 degrees, and adjust from there as quickly as I can. Then pay close attention to the VCC as well as the VS. Letting the VCC get to far from zero makes it much harder to maintain the VS at zero, so make half-degree adjustments to the AoA and keep the VCC at less then 10m/s absolute value.
As your velocity decreases, you will need to increase the AoA to maintain altitude. As you get the velocity down under 8 km/s your AoA will be up to about 80 degrees, and it's time to begin turning upright. Once "right side up" and velocity is less than 7.5 km/s it becomes a "normal" re-entry.
IMPORTANT TIP: The XR, by default, "locks out" certain AoA and bank settings, you will need to modify the XR's configuration to allow 80 degrees AoA at all bank angles, and to allow ALL bank angles (by default, bank angles between 60 and 120 are "locked out"). Refer to the XR series documentation for instructions on this.
This all requires practice, but in time you will be able to make unpowered entry and deadstick landings from Mars or even father.
