Yeah the SG05 and 06 are very similar I believe, not 100% sure on what the differences are. I think it's just they've added a fascia on the 06 which means the front fan intakes from the sides rather than directly, so you don't see it.
Your motherboard would be better paired with a K series processor, as it would allow you to overclock by adjusting the multiplier, however neither the processor you spec'd nor the one I did are K series so wont allow this anyway.
My board and the Wi-Fi dongle come in £33 cheaper (you'd need a Bluetooth dongle as well if that's something you require), that's the only reason I chose it. Your board would have course allow you to drop in a K series later on, if you wanted to, and, with a better cooler, overclock. But there lies the difficulty, finding a better cooler to keep things quieter and/or overclock a bit.
I've actually got the Z77 version of the board you chose. I've paired mine with an Corsair H80 cooler, which is great, but not all ITX cases can fit them (I haven't decided on which case I want yet, seriously considering the FT03-Mini). I believe from a little looking around it should fit in the SG05 and therefore likely in the SG06 too, however you lose the drive cage and the optical drive bay. The SSD you can get creative with, the optical drive however is probably rather a requirement of an HTPC.
I did consider something like the below, but didn't post it as it's a little bit larger than the SG05/06. This build, being an ATX PSU, also has more power available to run a beefier graphics card (up to 620 watts would easily fit), and more room in the case for a longer card.
I believe the Cooler Master Elite 120 should allow an H80 in place of the hard drive cage whilst still allowing you to keep a 5.25" bay, the adapter then allowing you to fit your slim slot-load blu-ray drive and the SSD underneath it in the 5.25 bay.
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Intel Core i5-4440 3.10GHz (Haswell) Socket LGA1150 Processor - Retail £139.99
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