I have the Sena and I too fumbled around with different components until I found a system that worked for me. For me, the intercom function is mute, as 80% of the riding I do is solo, and the 20% I do ride with others, they don't use communicators.
I first started with a Scala Q2 as the Sena wasn't out yet. I used it for 2 seasons and used it for phone and MP3. The phone function worked fantastic with the unit, and I used the cord hooked to my iPod for MP3's and did the earphone jack mod on it w/earbuds so the music sounded decent, and also functioned as earplugs.
Well, when I bought the FJR I wanted to add GPS in the mix and get rid of the cord going to the MP3 so I bought the Sena. I didn't have a GPS yet when I bought the Sena, but soon shortly decided on the Nuvi 765T to be my MP3 player and GPS. I never had any qualms with the Sena with that set up, my frustration was with the Nuvi. The Nuvi worked with the hands free technology, but was extremely flakey. The bluetooth only worked for about 20 hands free inputs, then the audio would start skipping like a scratched cd, which resulted in having to drop the Sena from the GPS and reconnecting it, fairly annoying if you want to skip thru a bunch of tracks. Also, the Nuvi wasn't performing as a GPS like I wanted and wouldn't pair with the phone via the Sena. I was frustrated with the whole set up, especially when trying to add the phone into the mix. It was extremely buggy and always locking up, having issues, etc. Also, it was a pain to pair both the Nuvi and the phone to the Sena as both shared the A2DP profile. Neither my phone nor the Nuvi was selectable in which profile you wanted, so you had to trick it by pairing the Nuvi first, then the phone second in order to get both to work.
After a 1,300 mile trip with the Nuvi bugging out several times, and it then becoming a consistent issue when used for more than 1 and a half consecutive hours I had finally had enough of the Nuvi. I shelled out the big bucks for the Zumo 665 and did the latest software update on it. I just completed a roughly 2,000 mile trip with it and am 90% happy with the set up.
The bluetooth works 100% better than it did with the Nuvi. The phone pairs beautifully with the Zumo and comes across nice and clear for both myself and the other person on the line with the Sena. I never once had an issue with skipping, or music not playing correctly, or it prioritizing correctly. Also, you don't have to worry about pairing sequence. Just turn everything on and it connects itself. AWESOME!
As a GPS, the 665 is also 10 times the unit the 765T was. Much more in depth routing preference options, much easier to use on the MC, etc. Only two downfalls with the 665. Map detail sucks when zoomed out. It takes a lot of scrolling at small increments to be able to look at nearby roads to see if they are paved, or are curvy, or connect to where you are wanting to go. This is no different, or might even be better than the Nuvi was though.
The second thing that sucks is that the handsfree bluetooth option doesn't work with the XM Radio. Being able to just push and hold the jog dial on the Sena to pause MP3's is awesome, if you want the music to mute in a hurry. I wish they would have incorporated the same handsfree technology to mute the XM radio. It is kind of a pain to mute the XM in a hurry, I usually just end up turning the volume down on the Sena.
Sorry, this has turned into an GPS review, but my comments on the Sena are: they designed it to work with the Zumo's, and it works wonderfully other than the XM mute issue. With the earbud mount, the music sounds great, phone calls work great, the jog dial beats any of the other controls on the other bluetooth units I have used hands down, and the battery lasts consistently 11+ hours(I was on the road 12.5 hours today and it did not die) with music playing 100% of the time. I have only had the Sena die once on me, and that was with the Nuvi set up, and it lasted 10.5 hours, but it does come with the nice long, coiled 12v charger that you can use to charge while using the headset(nice feature).
Overall, the Sena gets a thumbs up from me, although, it is designed to work with specific components. My work around with cheaper components, IE, the Nuvi, left undesired results. With the Zumo, I am happy, although I have almost $900 in hardware spent between the Zumo and the Sena as well as almost a $200/year XM radio subscription, but for me, it is worth it. I use it roughly 1 1/2 hours everyday just for commuting, let alone trips, and just being able to turn everything on(takes about 5 seconds) and it automatically pairing without me having to mess with sequence or anything is worth it for me.
YMMV