You really have to step up your game to counter that first wave.
I would imagine the best way to do this is practice: Figure out what works to defeat large enemies and what doesn't. For your rough game, you would practice on single player repulsing a 9.0 or even 9.3 (actually, do 9.3. If you counter that consistently, you can maybe handle 3 8.6 waves)
I have been subject to the blunt force for 3 or more waves. It's not easy, but doable. I would recommend waiting to build anything more then fighters until that first wave warning appears so that way you have a chache of resources. Then, when the wave warning appears, spend all your money building defenses just to counter that one wave. If the enemy is giving you more then your fair share of attention (especially ALL of the attention) then have your friends drop resources for you to build. Optimally, you have at least a MK I cap (I and II is best) of fighters before the 7 minute mark.
What and how you build your defense fleet and turrets is paramount. I would firstly recommend at least MK II gravity's. They will buy precious time and are as effective against 10 AI waves as 1. Space them between the home station and wormholes. All other turrets really must be built based on need: If lots of fighters: MLRS. Bombers? Lasers and missiles. Frigates? Basic turrets. Etc, etc.
EDIT: When the wave warnings pop up, it is also time to start building defense shields. One extra shield per wave is a decent rule. So if you have 3 waves incoming, you build 3 extra shields to defend the home.
It is important to have some MK I engineers at your home helping build as well so you can build quickly. If you go broke before you build at least 50 turrets then your friends need to help more.
EDIT: 8.6? That is meant to be rough from the start. Good luck!
1. It's already hard, good luck!
2. Gravity turrets
3. Fighter caps, I and II
4. Turrets built only once warning arrives to maximize your use
5. Friends give resources in proportion to wave distribution. All the waves on one player? That one player gets most of the resources.
6. If you want to learn to beat 3 8.6's consistently and deceively using single player, take a few spins of countering the first wave of a 9.3. For extra credit, do it with 2x waves.