I assume the H&K system has a more powerful amp? If i will need one, can anyone recommend a fairly cost effective one?

You will definitely benefit with an Amp if you want to get the best from your upgraded speakers because the amp in the basic HU is not so good (by today's standards).

Pioneer do a great little cheap one, it's a simple plug & play job (with BMW-ISO adapter), keeps all the stereo functionality as standard but greatly improves the sound quality.
Best price I've seen is on Amazon >

https://www.amazon.co.uk/gp/aw/d/B00PAQGYKE/ref=ox_sc_saved_image_4?smid=A1NFGBZ0PXC1X4&psc=1

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Or if you want slightly higher wattage: Vibe make one, same principle as the Pioneer above >

https://www.amazon.co.uk/Inex-Power...le/dp/B07MHHT1RL/ref=mp_s_a_1_1?dchild=1&keywords=iso+amp&qid=1585482715&sr=8-1

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And for a little more money: The Focus Impulse, again the same 'ghost' install principle as the others >

https://www.amazon.co.uk/Focal-Inte...B01EZYWW5M/ref=mp_s_a_1_7?dchild=1&keywords=focal+impulse&qid=1585483202&sr=8-7

<

 

I assume the H&K system has a more powerful amp? If i will need one, can anyone recommend a fairly cost effective one?

You will definitely benefit with an Amp if you want to get the best from your upgraded speakers because the amp in the basic HU is not so good (by today's standards).

Pioneer do a great little cheap one, it's a simple plug & play job, keeps all the stereo functionality as standard but greatly improves the sound quality.
Best price I've seen is on Amazon >

https://www.amazon.co.uk/gp/aw/d/B00PAQGYKE/ref=ox_sc_saved_image_4?smid=A1NFGBZ0PXC1X4&psc=1

<

Or if you want slightly higher wattage: Vibe make one, same principle as the Pioneer above >

https://www.amazon.co.uk/Inex-Power...le/dp/B07MHHT1RL/ref=mp_s_a_1_1?dchild=1&keywords=iso+amp&qid=1585482715&sr=8-1

<

And for a little more money: The Focus Impulse, again the same 'ghost' install principle as the others >

https://www.amazon.co.uk/Focal-Inte...B01EZYWW5M/ref=mp_s_a_1_7?dchild=1&keywords=focal+impulse&qid=1585483202&sr=8-7

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How easy are these amps to fit? The sound is awful in my m235i even after fitting uprated focal speakers!!

 

How easy are these amps to fit? The sound is awful in my m235i even after fitting uprated focal speakers!!

With an additional adapter like >

https://www.amazon.co.uk/Aerzetix-r...dp/B016DGE3ES/ref=mp_s_a_1_2?dchild=1&keywords=bmw+parrot&qid=1585645260&sr=8-2

< in theory it should be a simple case of plug and play without the need to cut or modify any of the car's wiring loom.
One problem could be trying to squeeze all the extra cables and connectors in the space behind the stereo and finding a suitable location behind the dash to fit the amp.

 

So you have to fit it behind the dash? Are there any plug and play replace amplifiers that don't require dismantling the dash?

 

Sorry, I wasn't very clear, they are designed to be hidden out of sight so could be mounted behind the dash, under the dash, in the glove box or under a seat (although the cables may require extending), etc. They're not very big so it should be easy enough to hide it somewhere - to be honest I've not looked into where I'm going to fit mine (yet)

 

I assume the H&K system has a more powerful amp? If i will need one, can anyone recommend a fairly cost effective one?

You will definitely benefit with an Amp if you want to get the best from your upgraded speakers because the amp in the basic HU is not so good (by today's standards).

Pioneer do a great little cheap one, it's a simple plug & play job (with BMW-ISO adapter), keeps all the stereo functionality as standard but greatly improves the sound quality.
Best price I've seen is on Amazon >

https://www.amazon.co.uk/gp/aw/d/B00PAQGYKE/ref=ox_sc_saved_image_4?smid=A1NFGBZ0PXC1X4&psc=1

<

Or if you want slightly higher wattage: Vibe make one, same principle as the Pioneer above >

https://www.amazon.co.uk/Inex-Power...le/dp/B07MHHT1RL/ref=mp_s_a_1_1?dchild=1&keywords=iso+amp&qid=1585482715&sr=8-1

<

And for a little more money: The Focus Impulse, again the same 'ghost' install principle as the others >

https://www.amazon.co.uk/Focal-Inte...B01EZYWW5M/ref=mp_s_a_1_7?dchild=1&keywords=focal+impulse&qid=1585483202&sr=8-7

<

This is super helpful, is the ISO adapter defo for the F22 2 series? It doesn't seem to be listed under compatible cars on the link you sent

https://www.amazon.co.uk/Aerzetix-r...dp/B016DGE3ES/ref=mp_s_a_1_2?dchild=1&keywords=bmw+parrot&qid=1585645260&sr=8-2

"BMW series1: E81 E82 E87 E88 /// BMW Serie3: E46 2002 -> /// BMW Serie3: E90 E91 E92 E93 /// BMW Serie5: E39, E60 / E61 /// BMW6 E63 E64 2004 -> /// BMW7: E65 E66 E67 E68 2001 -> /// BMW Mini 2000 -> /// BMW X3 (E83) 2004 -> /// BMW X5 E53 E70 /// BMW Z4 2003 -> /// BMW Z8 2000 -> /// Land Rover Defender 2 2001 -> /// Range Rover 2002-2006 /// Rover 2001->
XAD2-3 C4558"

 

This is super helpful, is the ISO adapter defo for the F22 2 series? It doesn't seem to be listed under compatible cars on the link you sent

https://www.amazon.co.uk/Aerzetix-r...dp/B016DGE3ES/ref=mp_s_a_1_2?dchild=1&keywords=bmw+parrot&qid=1585645260&sr=8-2

Pretty sure yes, that adapter is advertised for use with a Parrot (hence the compatibility list) but we would be repurposing it for our requirements I have been researching this for sometime now to do a very similar install in my F20 - the wiring diagram is the same for the F22 also.
However, depending on the spec of your headunit you will need to unclip the AUX and Telephone plugs (Blocks B & C in pic below) and possibly an optical cable (Block D) from the factory Quadlock and clip them into the corresponding empty locations on the aforementioned adapter.