My Myth boxes are an angry response to the Cable companies, Microsoft, Netflix, Tivo, etc. In other words, I'm just an angry little man.
Seriously though, I'm not sure the Myth boxes are the most efficient, or cheapest way to do things, but I kind of live for this sort of stuff.
Comcast pissed me off, so I looked for a way to ditch them. I now just go with OTA transmission in HD. I have an antenna in my attic, and I'm about 30 miles (straight line) from the main transmission tower in Chicago. So, it works really well for me.
ChannelMaster makes a DVR for OTA transmission that costs about $400.00. I figured I could build something better for that money.
So, my first Myth box was built with a dual core Intel processor (circa 2007-2008 processor??). It's more than enough processor and with a cheap NVidia 9800GT, I had a way overbuilt system. This system still serves as my backend. 4 GB of RAM as well.
Issues I ran into.
I started with Mythbuntu. Was pretty easy to setup. However, when I started adding applications, like Hulu Desktop, or even trying to play a Youtube video I ran into EXACTLY what you're talking about with only one application at a time being able to play audio. MythTV would lock down the audio.
Then I ran into another problem. My backend was downstairs in a finished basement on our bigger TV (52"). This was in hopes that we could save the upstairs of the house from the tortures inflicted by children. The upstairs has a 50". My wife and the kids love Netflix. Netflix doesn't play on Linux, so I had an HTPC running Windows XP.
Since I didn't have cable anymore, I had a choice of running another RG6 run to the upstairs TV from the Antenna, or network to the backend. If I networked, I would use MythTV again, but I would lose Netflix, and I would have to figure out the audio issue.
Netflix was workable through a virtual machine, but that would require a more modern computer. So, I spent a few bucks and went out and bought an AMD FX-4100 and a NVidia GT440 card at Microcenter for pretty cheap.
I was using MythTV 0.24 release, and I noticed that PulseAudio wasn't really supported and that it really only liked the ALSA drivers. Mythbuntu added the extra layer of Pulse Audio on top of ALSA, and I figured that's probably where the conflict arose between applications.
That's why I tried out ArchLinux. I'd be able to monitor conflicts because nothing would be on the computer that I didn't put on. Built up the main O/S, threw XFCE onto it, then built MythTV on top of that. Created a Button directly in the main menu to access my Virtual Machine with XP on it for Netflix and I was golden. I also have browser capability for Hulu, Amazon Video, Crackle, etc, etc along with DVD capability.
Now, that computer operated as just a frontend. The backend still used Mythbuntu. I did confirm that my fronted didn't have the audio conflicts, and everything played fine. I did need to configure my .asoundrc file though, but I was just using ALSA and it went pretty seamless.
My wife requested that I figure out the backend so we could have Netflix downstairs as well, because we are determined to get the kids into the basement instead of trashing the main floor. The kids LOVE Netflix (they are 5 and 3 currently).
So, I started a fresh load of ArchLinux onto the backend machine. Much more complicated than getting the frontend up and running. I eventually got it though, and now both machines are fairly identical, running rolling release distributions.
Two days ago though, while everything had been working fine, the audio started behaving the same way. I could only get audio from MythTV and nothing else. So I dug around and updated my .asoundrc file utilizing "dmix" and it's working again. In the process though, I found that MythTV 0.25 supports PulseAudio, and I found some tutorials that fix the audio issue revolving around Pulse Audio.
So, Mythbuntu is probably more workable than it was in the past. However, if I was to do it again all over, I'd still use Arch, just because I like knowing where everything is, and I'm not getting conflicting files, in varying directories, etc. While nothing is plug and play, I know exactly where everything is that I've modified or configured. I never got LIRC to work plug and play the way Mythbuntu has it installed, but with Arch I could manually configure it much easier than breaking through the layers that Mythbuntu had installed, these are all little things that took extra time, but I found with Mythbuntu, I was taking that time anyway because not everything was as plug and play as it was designed to be.
Also, I don't use LIRC anymore. I use this keyboard. http://www.siig.com/it-products/keyboards/wireless/wireless-mini-multimedia-trackball-keyboard.html
The kids do very well with it, and it makes navigating the web very easy. Also, configuring hotkeys for a keyboard in MythTV is much easier than configuring keys in LIRC (IMO).
For tuners in the backend, I started with an Hauppauge HVR-1600, then added a HVR-2250. The 2250 is a royal pain, and gives me headaches sometimes. This was all bought before the HD Homerun was really that well supported. If I were to do it again, I'd TOTALLY go with the HD Homerun. One box, three tuners, one cable and everything just networked. Much simple solution IMO.
Ultimately though, the real appeal is that I only have one box sitting under the TV instead of a DVR, a DVD player, a Roku, etc.