Fukuoka to Osaka

I have travelled to Japan numerous time and each time missed out on exciting places. This time I could like to asked an experience traveller for some guidance. My journey begins from Fukuoka Hakata JR Station and armed with JR Sanyo Sanin Area Pass in early April. Please advise on an exciting journey and where to stay along the way. I have only Six days. I have been to Hiroshima, Osaka, Kyoto,Himeji,Nara,Kobe. I am looking for other exciting places. Thank you

It looks like you've been to the more popular places in southern Kyushu, but there are still many good places to see...a lot depends on what you call 'exciting' though.
Beginning with your starting point Fukuoka, there are many open parks, shopping, seaside historical areas, and urban neon. One of the very best though is totally off the tourist radar - go see the Nanzoin temple about 20 minutes from Hakata Stn by train. Totally mind-blowing and free:
https://www.youtube.com/watch?v=lT4VQFmHFyM
See this site as a good guide:
http://www.thejapanfaq.com/fukpic.html
There are also many useful videos to give you a preview:
https://www.youtube.com/playlist?list=PL7LcPcmoSg-j4RLa6iC7ayvBAbOn8-0...
Look into a Fukuoka Tourist City Pass also:
http://yokanavi.com/access_tourist_eg
Be sure to try the tonkotsu ramen at least once, and see the wooden Great Buddha:
https://www.youtube.com/watch?v=hug3tCMvu28
You will likely be there in cherry blossom season and there are a number of good places, like Maizuru Koen and Nishi Koen:
https://www.youtube.com/watch?v=968CH00PboY
https://www.youtube.com/watch?v=y-pJPZjNVx0

Kitakyushu has a number of places often overlooked, including Kokura Castle, the Moji Retro area, and Sarakurayama, a mountaintop view that's one of the finest in Japan (and unknown to most self-proclaimed experts):
https://www.youtube.com/watch?v=Hl1pCW9Ibbk
One of the finest places you can see though is the Akiyoshido Cave and Akiyoshidai Plain. It's the biggest limestone cave in Japan and 300 million years in the making. Stunning.
Hagi may not be exciting, but offers a number of historic and interesting places to see.
Iwakuni is a nice half day trip to see the iconic bridge and mountaintop castle. Also very nice during cherry blossom season.
https://www.youtube.com/watch?v=0COOZXi66mM
Onomichi is a nice, off the beaten path place few tourists go see - some know its temple tour but fewer still go to see one of the finest temples in the area - Kosanji. Some describe it like a Buddhist Disneyland:
https://www.youtube.com/watch?v=97Q5EjEOXI8
Kurashiki is another choice - maybe not exciting, but known for its canals.
Takamatsu is a splendid place to visit, with the beautiful Ritsurin Garden and other sites. Also along the way is one of the best half day hikes you will ever take, at Kotohira. The shrine and view from the top is great, but the trek up is the real adventure:
https://www.youtube.com/watch?v=ley9rVIewoQ
Okayama is also a nice overlooked place too. Korakuen and Handayama are two beautiful gardens worth the time to see:
https://www.youtube.com/watch?v=5zAI3_N7NEM
https://www.youtube.com/watch?v=JGQ8o7k9GbA
Plus there is the castle, Kirin beer park and the Sapporo Winery.
These are along the Sanyo side and easiest to reach. The Sea of Japan side has good sites too, but more time consuming to get to, such as the Iwami Ginzan silver mine, Izumo shrine, Adachi Museum/Garden, Matsue, Tottori sand dunes, etc.

I should say southern Honshu, sorry.

Thank you Ken. I am looking at some of the places you have suggested. The usual problem are the once reaching the outback areas its difficult to find cheaper lodging or any lodging at all for example Miyajima. Do you have a strategy whereby looking for accommodation in this outback places?

Miyajima is somewhat special, because it is kept purposefully underdeveloped, there is a limited range of accomodations available on the island itself. Most other small to medium cities have cheap business hotels, at least some of which can be booked in English through booking.com or Rakuten Travel.

Only if you want something in the far remote countryside, or maybe very specific types of traditional accomodation can it be a challenge to find lodging.

For larger or medium sized cities, there is usually one chain business hotel I look for, such as Toyoko Inn, Super Hotel, Comfort Inn, and so on.
http://www.comfortinn.com/sitemap-japan-JP
http://www.toyoko-inn.com/eng/
http://www.superhoteljapan.com/en/
There are others of course, like Dormy Inn, Route Inn, etc. For Hagi, I stayed at the Royal Intelligent Hotel, one of the finest budget hotels I have ever been in. And for being in the butt-end of the country, in the morning I was uploading pics/video at 60Mb/sec! Wow! For some areas they are just a day trip, like Akiyoshido, and I stayed in nearby cities like Yamaguchi City. But others like Izumo, Matsue amd Tottori also have a business hotel listed above. As mentioned, Miyajima is an exception, and I stayed in Hiroshima City.
Accommodations are really not a problem off season, although even for outlying areas if you are there on a weekend, try to make a reservation as soon as you can - they can be full too.